Skip to main content

Full text of "Quain's elements of anatomy"

See other formats


MEMCAL 




John Marshall Williamson 
Mwnofial 



QUAIN'S ANATOMY. 



QUAIN'S 

ELEMENTS OF ANATOMY 



EDITED BY 

WILLIAM SHARPEY, M.D, F.E.S. 

PROFESSOR OF ANATOMY AND PHYSIOLOGY IN UNIVERSITY COLLEGE, LONDON 

ALLEN THOMSON, M.D., F.R.S. 

PROFESSOR OF ANATOMY IN THE UNIVERSITY OF GLASGOW 
AND 

JOHN CLELAND, M.D. 

PROFESSOR OF ANATOMY IN QUEEN'S COLLEGE, GALWAY 



IN TWO VOLUMES 

ILLUSTRATED BY UPWARDS OF 800 ENGRAVINGS ON WOOD. 



VOL. II. 



LONDON 

JAMES WALTON 

BOOKSELLER AND PUBLISHER TO UNIVERSITY COLLEGE 

137, GOWKR STREET. 

1867. 



LONDON : 
BRADBURY, EVANS, AND CO., PRINTERS, WHITEFRTARS. 



5 .*" .!.*** 




CONTENTS OF THE SECOND VOLUME. 

DIVISION L SYSTEMATIC AND DESCRIPTIVE ANATOMY 

(CONTINUED). 



PAGE 

SECTION V. NEUROLOGY . 501 

I. THE CEREBRO-SPINAL Axis . 501 

A. THE SPINAL CORD . . . 502 
Its description . . . 5 2 
Internal structure . . . 507 
Central Canal . . . 5 8 
Minute structure of the Cord . 509 
Origin of the Spinal Nerves . 511 

B. THE ENCEPHALON . . . 513 
The Medulla Oblongata . . 514 

Course of fibres through the 

Medulla . . . . 518 
Grey matter of the Medulla 5 19 
The Pons Varolii and Cerebel- 
lum 521 

Pons Varolii . . .521 
The Cerebellum . . . 522 
Its internal structure . 526 
The Cerebrum . . . . 529 
Exterior of the Cerebrum . 529 
Cerebral Convolutions . 531 
Base of the Cerebrum . . 53^ 
Internal parts of the Cere- 
brum . . . . 54 
Lateral Ventricles . . 543 
Third Ventricle . 55 
Internal Structure of the 

Cerebrum . . . 554 

"White matter . . . 555 

Grey matter . . , 559 
Membranes of the Brain and 

Spinal Cord . . . 562 
Dura Mater . . .562 

Pia Mater . . . . 564 

Arachnoid Membrane . . 565 
Blood-vessels of the Brain and 
x Spinal Cord . . .567 
Size and Weight of the Ence- 

phalon .... 568 
Weight of the several parts of 

the Encephalon . . . 571 

Weight of the Spinal Cord . 572 
Specific Gravity of the Ence- 
phalon . . . .572 



Development of the Cerebro- 
Spinal Axis . . . 
of the Spinal Cord 
of the Encephalon . . . 
of the membranes of the En- 
cephalon. 

II. THE CEREBRO-SPINAL NERVES 
A. CRANIAL NERVES 

Connections of the Cranial 
Nerves with the Encephalon 
Distribution of the Cranial 
Nerves . ... 

Olfactory Nerve 
Optic Nerve . . . . 
Third Pair of Nerves . 
Fourth Pair of Nerves . . 
Fifth Pair of Nerves 

Ophthalmic Nerve . . . 
Lachrymal Branch . 
Frontal Branch . . . 
Nasal Branch . 
Ophthalmic Ganglion . . 
Superior Maxillary Nerve . 
Orbital branch 
Posterior Dental Branches 
Anterior Dental Branch . 
Infraorbital Branches 
Spheno - palatine Gang- 
lion . . . . 
Inferior Maxillary Nerve . 
Deep Temporal, Masse- 
teric, Buccal, and Ptery- 
goid Branches . . 

Auriculo-temporal Nerve 
Gustatory Nerve . . 
Inferior Dental Nerve 
Otic Ganglion 
Submaxillary Ganglion . 
Sixth Pair of Nerves 
Seventh Pair of Nerves . . 
Facial Nerve 

Connecting Branches . . 
ChordaTyinpani and Nerve 

to the Stapedius . 
Posterior Auricular Branch 



PAGE 

573 

574 
575 

581 
582 
582 

583 

587 

592 

592 

593 

594 

595 

597 

597 

59 

5 

599 
600 
600 
60 1 
60 1 
602 

603 
605 



605 
606 
606 
608 
608 
609 
610 
610 
610 
611 

611 
612 



VI 



CONTENTS. 



PAGE 

Digastric and Stylo-hyoid 

Branches . . .613 

Temporo-facial Division . 613 

Cervico-facial Division . 613 

Auditory Nerve . . .615 

Eighth Pair of Nerves . . 615 

Glosso-pharyngeal Nerve . 615 

Connecting Branches and 

Tympanic Branch . 616 
Branches distributed in 

the Neck . . . 617 

Pneumo-gastric Nerve . 618 
Connecting Branches and 

Auricular Branch . 621 
Pharyugeal Branch . .621 

Superior Laryngeal Branch 621 
Recurrent Laryngeal 

Branch . . .622 

Cardiac Branches . . 623 

Pulmonary Branches . 623 

(Esophageal Branches . 623 

Gastric Branches . . 623 

Spinal Accessory Nerve . . 625 

Ninth Pair of Nerves . . 626 

Connecting Branches . . 626 

Muscular and Lingual 

Branches . . . 626 

B. SPINAL NERVES . . . . 628 

Roots of the Spinal Nerves . 630 
Posterior Primary Divisions of 

the Spinal Nerves . . 632 

Suboccipital Nerve . . 632 

Cervical Nerves . . . 633 

Dorsal Nerves . . . 634 

Lumbar Nerve . . . 634 
Sacral Nerves . . .635 

Coccygeal Nerve . . . 635 
Anterior Primary Divisions of 

the Spinal Nerves . . 635 

Cervical Nerves . . . 636 

Suboccipital Nerve . . 636 

Second Cervical Nerve . 636 

Cervical Plexus . . . 636 

1. Superficial Ascending 

Branches . . 638 

Superficial Cervical 

Nerve . . .638 
Great Auricular Nerve 638 
Small Occipital Nerve 638 

2. Superficial Descending 

Branches . . 639 
Supraclavicular Nerves 639 

3. Deep Branches : Inner 

Series . . 640 

Muscular Branches 640 

Phrenic Nerve . 640 

4. Deep Branches : Exter 

nal Series . 641 

Brachial Plexus . . 641 
Branches above the Cla 

vicle . . . 643 

Posterior Thoracic Nerve 644 

Suprascapular Nerve . 644 

Branches below the Clavicle 644 



PAGE 

Anterior Thoracic Nerve 645 
Subscapular Nerve . 645 
Circumflex Nerves . 645 
Internal Cutaneous 

Nerve . . . . 646 
Small Internal Cuta- 
neous Nerve . . 646 
Musculo- cutaneous 

Nerve . . . 648 

Ulnar Nerve . . 648 
Median Nerve . . 649 
Musculo-spiral Nerve 652 
Radial Nerve . . 653 
Posterior Interosseous 

Nerve . .^ . . 654 
Anterior Primary Divisions of 

the Dorsal Nerves . -655 
First Dorsal Nerve . . 655 
Upper or Pectoral Intercostal 

Nerves . -655 

Lower or Abdominal Inter- 
costal Nerves . . . 657 
Last Dorsal Nerve . . 658 
Anterior Primary Divisions of 

the Lumbar Nerves . 658 
Lumbar Plexus . . . 658 
Ilio-hypogastric and Ilio- 

inguinal Nerves . . 660 

Genito- crural Nerve . . 660 

External Cutaneous Nerves 662 

Obturator Nerve . . 662 

Accessory Obturator Nerve 663 

Anterior Crural Nerve . 664 

Muscular Branches . . 665 

Middle Cutaneous Nerve 665 

Internal Cutaneous 

Nerve . . . 665 
Internal Saphenous 

Nerve . . . 666 
Fifth Lumbar Nerve . . 667 
Superior Gluteal Nerve . 667 
Anterior Primary Divisions of 
the Sacral and Coccygeal 
Nerves .... 668 
The Sacral Nerves . . . 668 
Fourth Sacral Nerve . . 668 
Fifth Sacral Nerve . . 668 
Coccygeal Nerve . . 668 
Sacral Plexus . . . 669 
Muscular Branches . .670 
Pudic Branches . . . 670 
Small Sciatic Nerve . 673 
Great Sciatic Nerve . . 675 
Internal Popliteal Nerve 676 
External or Short Saphe- 
nous Nerve . . 677 
Posterior Tibial Nerve 677 
Internal Plantar Nerve 677 
External Plantar Nerve 679 
External Popliteal or 

Peroneal Nerve . 679 
Musculo -cutaneous 

Nerve . . . . 680 
Anterior Tibial Nerve . 68 1 



CONTEXTS. 



Vll 



Synopsis of the Cutaneous Dis- 
tribution of the Cerebro- 

spinal Nerves . . . 682 
Synopsis of the Muscular Dis- 
tribution of the Cerebro- 

spinal Nerves . . . 684 
Muscles of the Head and 

Fore Part of the Neck . 684 
Muscles belonging exclu- 
sively to the Trunk, and 
Muscles ascending to the 

Skull 684 

Muscles attaching the Upper 

Limb to the Trunk . . 685 

Muscles of the Upper Limb 685 

Muscles of the Lower Limb 686 

III. SYMPATHETIC NERVES . . 686 

A. GANGLIATED CORDS . . 688 
Cervical Part . . . . 688 

Upper Cervical Ganglion . 688 
Ascending Branch and 

Cranial Plexuses . . 688 
Pharyngeal Nerves and 

Plexus . . . . 690 

Upper Cardiac Nerve . 690 

Branches to Blood-vessels 692 

Middle Cervical Ganglion . 692 

Lower Cervical Ganglion . 693 

Thoracic Part . . . 693 

Branches of the Ganglia . 693 

Great Splanchnic Nerve . 695 

Small Splanchnic Nerve . 696 

Smallest Splanchnic Nerve . 696 

Lumbar Part . . . 696 

Sacral Part . . . . 696 

Coccygeal Gland . .697 

B. GREAT PLEXUSES OF THE SYM- 

PATHETIC . . . 698 

Cardiac Plexus . . . 698 

Superficial . . . . 698 

Deep 698 

Solar or Epigastric Plexus . 699 

Aortic Plexus . . . 702 

Hypogastric Plexus . . . 702 
Pelvic Plexus . . .703 

IV. ORGANS OF THE SENSES . . 705 
THE EYE 705 

Appendages of the Eye . . 705 

Eyelids and Conjunctiva . 705 

Lachrymal Apparatus . . 709 

Globe of the Eye . . .710 

External Coat of the Eyeball . 711 
Sclerotic Coat . . .711 

Cornea . . ... 714 

Middle Tunic of the Eyeball . 716 
Choroid Coat . . .716 

Iris 718 

Ciliary Muscle, Ligamentum 
Pectinatum, and Circular 
Sinus . . . .721 
Vessels and Nerves of the 

Middle Tunic of the Eye . 721 

Retina or Nervous Tunic . 725 

Structure of the Retina . 726 



PAGE 

Vitreous Body . . . . 731 

The Lens and its Capsule . 733 

Lens 733 

Suspensory Ligament of the 

Lens, and Canal of Petit 736 
Aqueous Humour and its 

Chamber . . . 736 

Development of the Eye . 736 

THE EAR 740 

External Ear .... 740 

Pinna 740 

External Auditory Canal . 743 

Middle Ear or Tympanum . 744 

Small Bones of the Ear . 748 
Ligaments and Muscles of 

Tympanum . . . 749 
Lining Membrane of Tym- 
panum . . . 75 1 
Vessels and Nerves of Tym- 
panum . . . . 752 
Internal Ear or Labyrinth . 753 
Osseous Labyrinth . . 753 
Membranous Labyrinth . 757 
Vestibule . . . 757 
Semicircular Canals . . 75& 

Cochlea 760 

Blood-vessels of Labyrinth . 767 

Development of the Ear . 768 

NOSE 771 

Cartilages of Nose . . .771 

Nasal Fossae . . . . 773 

Mucous Membrane . . 774 

Development of the Nose . . 778 

SECTION VI. SPLANCHNO- 

LOGY 779 

ORGANS OF DIGESTION . . 779 

Mouth 779 

Teeth 780 

Structure . ... 784 

Development of Teeth . 792 

Tongue 805 

Mucous Membrane . . 805 

Muscular substance . . 809 

Palate 813 

Tonsils 813 

Salivary Glands . . .815 
Parotid Gland . . . 815 
Submaxillary Gland . . 816 
Sublingual Gland . . . 817 
Pharynx .... 819 
(Esophagus . . . . 821 
Abdominal Digestive Organs . 823 
Abdomen ..... 823 
Parts situated in each Re- 
gion of the Abdomen . 826 
The Peritoneum . . . 826 
Stomach .... 830 
Structure of coats . . 832 
Small Intestine . . .838 
Structure of Small Intes- 
tine . . . . 841 
Large Intestine . . . 851 
Caecum . ... 852 



viii 



CONTENTS. 



PAGE 

Colon .... 853 

Rectum . . . . 856 

Anus and its Muscles . 859 
Development of the Alimentary 

Canal and Peritoneal Cavity 859 

Liver ..... 862 

Structure of Liver . . . 869 
The Bile . . . .878 
Development and Foetal 

Peculiarities of Liver . 879 

Pancreas . . . . . 88 1 

Spleen 883 

ORGANS OF RESPIRATION . . 888 

Trachea and Bronchi . . 888 

Structure of the Trachea . 890 

Pleurae 892 

Lungs .... 894 

Root of Lung . . . 897 

Structure of Lungs . . 898 
Development of Lungs and 

Trachea .... 904 

Larynx or Organ of Voice . . 905 

Cartilages of Larynx . . 905 

Muscles of Larynx . . . 914 

Vessels and Nerves of Larynx 919 
Development and Growth of 

Larynx . . . -919 
DUCTLESS GLANDS ON THE 

LARYNX AND TRACHEA . 920 

Thyroid Body . . . 920 

Thymus Gland . . . 923 

URINARY ORGANS . . . 926 

Kidneys .... 926 

Suprarenal Bodies . . . 939 



PAGE 

944 
952 
952 
952 
952 
955 
956 
958 
959 

963 
963 



Ureters .... 
Urinary Bladder . . . 
Urethra .... 
ORGANS OF GENERATION . . 
MALE ORGANS 

Prostate Gland . . . 
Penis .... 
Corpora Cavernosa . . 
Corpus Spongiosum 
Urethra of the Male . . 
Testes and Excretory Appa- 
ratus .... 
Coverings of Testis and 
Cord .... 
Vessels and Nerves of the 
Coverings of the Testis 
and Cord . . . 967 
Testes . . . . 967 
Vas Deferens . . . 971 
Seminal Vesicles and 

Ejaculatory Ducts . . 973 
Vessels and Nerves of 

Testis. . . .975 

FEMALE ORGANS . . . 977 

Vulva .... 977 

Female Urethra . . . 980 

Vagina .... 980 

Uterus . ... 982 

Ovaries and Fallopian Tubes 988 

Development of the Urinary 

Organs .... 992 
Development of the Organs 

of Generation . . . 995 
MAMMARY GLANDS . . 1002 



DIVISION II. SURGICAL ANATOMY. 



SURGICAL ANATOMY OF THE 
ARTERIES 

Common Carotid Artery 

Subclaviau Artery 

Brachial Artery . 

Common Iliac Arteries 

Internal Iliac Artery . 

External Iliac Artery 

Femoral Artery . 
SURGICAL ANATOMY OF THE PARTS 



1005 
1005 
,1007 
1010 

1012 
1014 
1014 
IOI5 



CONCERNED IN CERTAIN ABDO- 
MINAL HERNLE . . . 1018 

The Parts concerned in Inguinal 
Hernia ..... 1018 

Inguinal Hernise . . . . 1025 

The Parts concerned in Femoral 
Hernia 1031 

Femoral Hernia . . . . 1034 
THE PERINEUM AND ISCHIO-RECTAL 

REGION 1037 

Lateral Operation of Lithotomy 1043 



DIVISION III. DISSECTIONS. 



GENERAL MANAGEMENT OF THE 

DISSECTIONS .... 1047 
SPECIAL DIRECTIONS FOR THE DIS- 



SECTION OF EACH PART 
Head and Neck 



1048 
1048 



Upper Limbs or Superior Extre- 
mities . . . . . 1059 

Thorax 1066 

Abdomen and Pelvis . . . 1069 
Lower Limbs or Inferior Extre- 
mities 1078 



NEUROLOGY. CEREBRO-SPINAL AXIS. 501 



SECTION V. NEUROLOGY. 

UNDER the name of Neurology, it is intended to include the descriptive 
anatomy of the various organs forming parts of the nervous system. 

The nervous system consists of two sets of parts, one of which is eentral, 
the other peripheral. To the first set belong the brain and spinal cord, 
forming together the cerebro-spinal axis, and the ganglia : to the second 
set belong all the nerves distributed throughout the body ; and along with 
these may be included the organs of the senses, or those organs which 
contain the terminations of the several nerves of special sensation, in con- 
nection with certain apparatus or modifications of structure related to the 
reception of impressions by each of these nerves. 

Among the peripheral nerves it is necessary also to distinguish the cere- 
bro-spinal and the sympathetic or ganglionic, which, though intimately 
connected with each other at some places, are yet so different in their 
structure and mode of distribution as to require separate description. 

The description of these several parts of the nervous system will be 
brought under the following four subsections, viz. 1. The cerebro-spinal 
axis ; 2. The cerebro-spinal nerves and the ganglia connected with them ; 
3. The sympathetic nerves and their ganglia ; 4. The organs of the 
senses. 

I. THE CEREBRO-SPINAL AXIS. 

The cerebro-spinal axis is contained partly within the cavity of the cra- 
nium, and partly within the vertebral canal ; it is symmetrical in its form 
and structure throughout, consisting of a right and a left half, separated 
to a certain extent by longitudinal fissures, and presenting in their plane of 
union various portions of white and grey nervous substance which cross 
from one side to another, and form the commissures of the brain and spinal 
cord. 

Enclosed within the skull and the vertebral canal, the cerebro-spinal axis 
is protected by the bony walls of those tw6 cavities ; it is also surrounded 
by three membranes, which afford it additional protection and support, and 
are subservient to its nutrition. These envelopes, which will be described 
hereafter, are, 1st, a dense fibrous membrane named the dura mater, which 
is placed most superficially ; 2nd, a serous membrane called the arach- 
noid ; and, 3rd, deepest of all, a highly vascular membrane named the pia 
mater. 

The cerebro-spinal axis is divided by anatomists into the encephalon or 
enlarged upper mass placed within the cranium, and the spinal cord con- 
tained within the vertebral canal. 

These two parts have a relation, one to the other, very similar to that 
which subsists between the cranium and vertebral column : thus, they are 
continuous structures ; at the time of their first formation in the foetus they 
are nearly similar ; the earliest developed distinction consists in the enlarge- 
ment of the encephalon ; and, moreover, the spinal cord, like the vertebral 
column, continues to present a structure nearly uniform throughout its 
extent, while the encephalon becomes gradually more and more complicated, 



502 



THE SPINAL COED. 




till at last it is difficult to trace the 
serial relation of its constituent 
parts, or any correspondence with 
the structure of the cord. 

Fig. 339. VIEW OP THE CEREBRO- 

SPINAL AXIS OF THE NERVOUS SYSTEM 

(after Bourgery). -g- 

The right half of the cranium and 
trunk of the body has been removed by 
a vertical section ; the membranes of the 
brain and spinal marrow have also been 
removed, and the roots and first part of 
the fifth and ninth cranial, and of all 
the spinal nerves of the right side, have 
been dissected out and laid separately on 
the wall of the skull and on the several 
vertebrae opposite to the place of their 
natural exit from the cranio-spinal 
cavity. 

F, T, 0, lateral surface of the 
cerebrum ; C, cerebellum ; P, pons 
Varolii ; m o, medulla oblongata ; m s, 
upper and lower extremities of the spinal 
marrow ; c e, on the last lumbar ver- 
tebra, marks the cauda equina ; v, the 
three principal branches of the nervus 
trigeminus or fifth pair ; C I, the sub- 
occipital or first cervical nerve ; above 
this is the ninth pair ; C vm, the eighth 
or lowest cervical nerve ; D I, the first 
dorsal nerve ; D xii, the last or twelfth ; 
L i, the first lumbar nerve ; L v, the last 
or fifth ; S I, the first sacral nerve ; S v, 
the fifth ; Coi, the coccygeal nerve ; s t 
the left sacral plexus. 

A. THE SPINAL CORD. 

The spinal cord, or spinal marrow 
(medulla spinalis), is that part of 
the cerebro- spinal axis which is 
situated within the vertebral canal. 
It extends from the margin of the 
foramen magimm of the occipital 
bone to about the lower part of the 
body of the first lumbar vertebra. 
It is continued into the medulla 
oblongata above, and ends below 
in a slender filament, the filum 
terminale or central ligament of the 
spinal cord. 

Invested closely by a proper 
membrane (the pia mater), the 
cord is enclosed within a sheath 
(theca) considerably longer and 
larger than itself, which is formed 
by the dura mater, and which is 
separated from the walls of the 



THE SPINAL CORD. 



503 



canal by numerous vascular plexuses, and 
much loose areolar tissue. The interval 
between the investing membrane and the 
sheath of the cord is occupied by a serous 
membrane (the arachnoid), and the space 
between the latter membrane and the pia 
mater is occupied by a fluid called the 
cerebro-spinal fluid. Within this space 
the cord is kept in position by proper 
ligaments, which fix it at different points 
to its sheath, and by the roots of the 
spinal nerves, an anterior and a pos- 
terior root belonging to each, which 
pass across the space from the surface of 
the cord towards the intervertebral fora- 
mina. From its lower part, where they 
are closely crowded together, the roots 
of the lumbar and sacral nerves descend 
nearly vertically to reach the lumbar 
intervertebral and the sacral foramina, 
and form a large bundle or lash of 
nervous cords named the cauda equina, 
which occupies the vertebral canal below 
the termination of the cord. 



A Fig. 340. 



-7 C 



10 



Fig. 340. ANTERIOR AND POSTERIOR VIEWS OP 
THE MEDULLA OBLONGATA AND SPINAL CORD 
WITH SECTIONS. ^ 

The cord has been divested of its membranes 
and the roots of the nerves. A, presents an 
anterior, B, a posterior view, showing the upper 
or brachial, and the lower or crural enlargements. 
In these figures the filiform prolongation, repre- 
sented separately in B', has been removed ; C, 
shows a transverse section through the middle of 
the medulla oblongata ; D, a section through the 
middle of the cervical enlargement of the spinal 
cord ; E, through the upper region of the dorsal 
part ; F, through its lower ; Gr, through the 
middle of the lumbar enlargement ; and H, near 
the lower end of its tapering extremity. 

1, anterior pyramids ; 1', their decussation ; 
2, olivary bodies ; 3, restiform bodies ; 4, pos- 
terior surface of the medulla oblongata ; 4', cala- 
mus scriptorius ; 5, posterior pyramids ; 6, pos- 
terior lateral columns passing up into the restiform 
bodies ; 7, 7, anterior median fissure extending 
through the whole length of the spinal cord ; 8, 8, 
anterior lateral groove ; 9, 9, posterior median 
fissure; 10, 10, posterior lateral groove; x, 
lower end of the tapering extremity of the cord ; 
x , x , in B', the filiform prolongation of the 
cord and its pia-matral covering. 

Although the cord usually ends near the 
lower border of the body of the first lumbar 
vertebra, it sometimes terminates a little above 
or below that point, as opposite to the last 



10- 



504 



THE SPINAL COED. 



dorsal or to the second lumbar vertebra. The position of the lower end of the cord also 
varies according to the state of curvature of the vertebral column, in the flexion 
forwards of which, as in the stooping posture, the end of the cord is slightly raised. 
In the foetus, at an early period, the cord occupies the whole length of the vertebral 
canal ; but, after the third month, the canal and the roots of the lumbar and sacral 
nerves begin to grow more rapidly than the cord itself, so that at birth the lower end 
reaches only to the third lumbar vertebra. 




Fig. 341. POSTERIOR VIEW OP THE MEDULLA OBLONGATA AND OP THE SPINAL CORD 
WITH ITS COVERINGS AND THE ROOTS OF THE NERVES (from Sappey). 4 

The theca or dura-matral sheath has been opened by a median incision along the whole 
length, and is stretched out to each side. On the left side, in the upper and middle parts 
(A and B), the posterior roots of the nerves have been removed so as to expose the liga- 
mentum denticulatum ; and along the right side the roots are shown passing out through 
the dura mater. The roman numbers indicate the different nerves in the cervical, dorsal, 
lumbar, and sacral regions : 9, several of the pointed processes of the ligamentum den- 
ticulatum ; 10, origin of several posterior roots ; 11, posterior median fissure ; 12, 
ganglia of the spinal nerves ; 13, part of the anterior roots seen on the left side ; 14, 
the united nerve ; 15, tapering lower end of the spinal cord; 16, filum terminale; 17, 
cauda equina. 

The length of the spinal cord is from fifteen to eighteen inches ; and it 
varies in diameter in different situations. Its general form is cylindrical, 
somewhat flattened before and behind. It presents two enlargements an 
upper or cervical, and a lower or lumbar. The cervical enlargement is of 
greater size and extent than the lower. It reaches from the third cervical 
to the first dorsal vertebra ; its greatest diameter is from side to side. 



FORM AXD POSITION OF THE COED. 



505 



The lower or lumbar enlargement is situated nearly opposite the last dorsal 

vertebra ; its antero-posterior diameter is nearly equal to the transverse. 

Below this enlargement, the cord tapers in 

the form of a cone, from the apex of which Fig. 342. 

the small filiform prolongation is continued 

downwards for some distance within the 

sheath. 



Fig. 342. LOWER PART OP THE SPINAL CORD WITH 
THE CAUDA EO.UINA AND SHEATH, SEEN FROM BE- 
HIND. 

The sheath has been opened from behind and 
stretched towards the sides ; on the left side all the 
roots of the nerves are entire ; on the right side both 
roots of the first aud second lumbar nerves are entire, 
while the rest have been divided close to the place of 
their passage through the sheath. The bones of the 
coccyx are sketched in their natural relative position 
to show the place of the filum terminale and the lowest 
nerves. 

a, placed on the posterior median fissure at the 
middle of the lumbar enlargement of the cord ; b, , 
the terminal filament, drawn slightly aside by a hook 
at its middle, aud descending within the dura-matral 
sheath ; b', b', its prolongation beyond the sheath 
and upon the back of the coccygeal bones ; c, the 
dura-matral sheath ; d, double foramina for the 
separate passage of the anterior and posterior roots of 
each of the nerves ; e, pointed ends of several pro- 
cesses of the ligamentum denticulatum ; Dx, and 
DXII, the tenth and twelfth dorsal nerves ; Li, and 
Lv, the first and fifth lumbar nerves; Sr, and Sv, 
the first and fifth sacral nerves; Ci, the coccygeal 
nerve. 

The cervical and lumbar enlargements have an 
evident relation to the large size of the nerves 
which supply the upper and lower limbs, and which 
are connected with those regions of the cord, in 
accordance with the general fact observed in the 
animal kingdom, that, near the origin of large nerves, 
the central nervous substance is accumulated in 
larger proportion. At the commencement of its 
development in the embryo the spinal cord is des- 
titute of these enlargements, which, in their first 
appearance and subsequent progress, correspond 
with the growth of the limbs. 

Sometimes the cord presents one or two bulbs or 
swellings towards its lower end. 

According to Foville, the lumbar enlargement is 
chiefly due to an increase in bulk of the anterior 
region of the cord. (Trait6 compl. de 1'Anat., &c., 
du Syst. Nerv. Cerebro-Spinal. Paris, 1844. Part 
I., p. 138.) 



"DXD 



Li 



St 



The terminal filament (filum terminale, cen- 
tral ligament) descends in the middle line 
amongst the nerves composing the cauda 

equina, and, becoming blended with the lower end of the sheath opposite to 
the first or second sacral vertebra, passes on to be fixed to the lower end of 

L L 



606 THE SPINAL COED. 

the sacral canal, or to the base of the coccyx. Internally, it is a prolongation 
for about half its length of some of the nervous elements of the cord ; 
externally, it consists of a tube of the pia mater or innermost membrane, 
which, being attached at its lower end to the dura mater and vertebral 
canal, keeps pace with the latter in its growth, whilst the cord relatively 
shortens. It is distinguished by its silvery hue from the nerves amid which 
it lies. Small blood-vessels may sometimes be seen upon it. 

Fissures. When removed from the vertebral canal, and divested of its 
membranes, the spinal cord is seen to be marked by longitudinal fissures. 
Of these, two, which are the most obvious, run along the middle line, 
one in front and the other behind, and are named the anterior and pos- 
terior median fissures. 

The anterior median fissure is more distinct than the posterior, and pene- 
trates about one-third of the thickness of the cord, its depth increasing 
towards the lower end. It contains a fold or lamelliform process of the pia 
mater, and also many blood-vessels, which are thus conducted to the centre 
of the cord. At the bottom of this fissure is seen the transverse connecting 
portion of white substance named the anterior white commissure. 

The posterior median fissure is less marked in the greater part of its 
extent than the anterior, but becomes more evident towards the upper part 
of the cord. In a certain sense it is no real fissure, except at the lumbar 
enlargement and in the cervical region, in both of which places a superficial 
fissure is distinctly visible ; for, although the lateral halves of the posterior 
part of the cord are quite separate, there is no distinct reflection of the pia 
mater between them, but rather a septum of connective tissue and blood- 
vessels which passes in nearly to the centre of the cord, as far as the posterior 
grey commissure. 

Besides these two median fissures, two lateral furrows or fissures have 
been described on each side of the cord, corresponding with the lines of 
attachment of the anterior and posterior roots of the spinal nerves. 

The posterior lateral fissure is a superficial depression along the line of 
attachment of the posterior roots, and is at the edge of the plane in which 
these roots pass inwards to the grey matter of the cord. 

The anterior lateral fissure, which is often described in the line of the 
origin of the anterior roots of the nerves, has no real existence as a groove. 
The fibres of these roots in fact, unlike the posterior, do not dip into the 
spinal cord in one narrow line, but spread over a space of some breadth. 
The grey substance of the cord, however, approaches the surface somewhat 
in the vicinity of the place where the anterior roots enter : and this, together 
with a slight depression, produces the appearance which has been described 
as a groove. Thus, each lateral half of the cord is divided by the posterior 
lateral fissure into a posterior and an antero-lateral column ; and although 
we cannot trace an anterior lateral fissure, this antero-lateral portion of the 
cord may, for the convenience of description, be considered as subdivided 
into an anterior and a lateral column by the internal grey matter. 

On the posterior surface of the cord, and most evidently in the upper 
part, there are two slightly marked longitudinal furrows situated one on 
each side, close to the posterior median fissure, and marking off, at least in 
the cervical region, a slender tract, named the posterior median column.. 
Between the anterior and posterior roots of the spinal nerves, on each side, 
the cord is convex, and sometimes presents a longitudinal mark correspond- 
ing with the line of attachment of the ligamentum denticulatum. 

Foville states, that in a new-born child there is a narrow accessory bundle of white 



INTERNAL STRUCTURE OF THE CORD. 



507 



matter, which runs along the surface of the lateral column, and is separated from it 
by a streak of greyish substance. According to the same authority, this narrow tract 
enlarges above, and may be traced upwards along the side ot the medulla oblongata 
into the cerebellum. (Op. cit. p. 285.) 



Fig. 343. 




Fig. 343. DIFFERENT 
VIEWS OF A PORTION OF 
THE SPINAL CORD FROM 
THE CERVICAL REGION 
WITH THE ROOTS OP 
THE NERVES. Slightly 
enlarged. 

In A, the anterior sur- 
face of the specimen is 
shown, the anterior nerve - 
root of the right side 
being divided ; in E, a 
view of the right side is 
given ; in C, the upper 
surface is shown ; in D, 
the nerve-roots and gan- 
glion are shown from 
below. 1, the anterior 
median fissure ; 2, pos- 
terior median fissure ; 3, 
anterior lateral depres- 
sion, over which the ante- 
rior nerve-roots are seen 
to spread ; 4, posterior 
lateral groove, into which 
the posterior roots are 
seen to sink ; 5, anterior 
roots passing the ganglion ; 
5', in A, the anterior root 

divided; 6, the posterior roots, the fibres of which pass into the ganglion, 6' ; 7, the 
united or compound nerve ; 7', the posterior primary branch seen in A and D, to be 
derived in part from the anterior and in part from the posterior root. 

Internal structure of the spinal cord. The spinal cord consists of white 
aiid grey nervous substance. The white matter, forming by far the larger 
portion of the cord, is situated externally, whilst the grey matter is dis- 
posed in the interior. 

The grey matter, as seen in a transverse section of any part of the cord, 
presents two crescent-shaped masses, placed one in each lateral half, with their 
convexities towards one another, and joined across the middle by a transverse 
portion, the grey or posterior commissure of the cord. Each of these grey 
crescents has an anterior and a posterior cornu or horn. The posterior, 
generally longer and narrower, approaches the posterior lateral fissure : the 
anterior, shorter and thicker, extends towards the place of attachment of the 
anterior roots of the nerves. In front of it a layer of white substance 
separates it from the bottom of the anterior median fissure, this is named 
the anterior white commissure. 

Another white layer, very thin and indistinct, was formerly described as lying 
behind the grey commissure; but in the present state of our knowledge it seems 
sufficient to describe one white commissure, and one grey commissure behind it. 

At the back part or tip of the posterior horn, which is somewhat en- 
larged, the grey matter has a peculiar semitransparent aspect, whence it 
was named by Rolando substantia cinerea gelatinosa : the remaining and 

L L 2 



508 



THE SPINAL CORD. 



greater part of the grey matter, which resembles that most generally preva- 
lent, was named by Rolando the substantia spongiosa. 

The grey cornua vary in form in different parts of the cord : thus they 
are long and slender in the cervical portion, still more slender in the dor- 
sal, and shorter and wider in the lumbar region. The grey matter appears 
in a series of sections to be, relatively to the white, more abundant in the 
lumbar region of the cord, less so in the cervical region, and least so in the 
dorsal. The actual amount, however, of white matter is greatest in the 
neck. Towards the lower end of the cord, the double crescentic form 
gradually disappears, and the grey matter is collected into a central mass, 
which is indented at the sides. At its extreme point, according to Remak 
and Valentin, the cord consists of grey matter only. 



Fig. 344. 



Fig. 




344. SECTIONS OF THE SPINAL 
CORD IN DIFFERENT PARTS. 



These views are taken partly from 
Stilling's plates and partly from nature. 

A, is a section through the middle of the 
cervical enlargement, at the root of the 
sixth cervical nerve; B, through the mid- 
dle of the dorsal cylindrical portion ; C, 
through the middle of the lumbar enlarge- 
ment ; D, in the conical diminishing part 
of the cord ; E, farther down at the 
origin of the fifth sacral nerve ; F, at 
that of the coccygeal nerve ; Gf, is a sec- 
tion of the part where the conus medul- 
laris begins to pass into the filum termi- 
nale ; and H, at the lower part of this 
or in the commencement of the filum 
terminale. 

A, B, and C, are fully twice the natural 
size ; D, E, and F, about three times ; 
and Gr and H, about six times. In A, 
and C, a, marks the .interior root- fibres 
of the nerves ; and p, the posterior root- 
fibres as they enter the spinal cord. In 
D, E, and F, the great diminution of the 
white substance in proportion to the grey 
is seen ; in G-, the peculiar form of the 
central canal and medullary substance 
covering it ; and in H, the open con- 
dition of the central canal posteriorly. 

In all the figures the position is the 
same, viz., the anterior part placed down- 
wards. 



Central canal. Extending through the whole length of the spinal cord, 
in the substance of the grey commissure, there is a minute central canal 
which in prepared transverse sections of the cord is barely visible, as a 
speck, with the naked eye. Superiorly, it is continued into and opens out 
at the calamus scriptorius of the fourth ventricle ; and inferiorly, it is 
prolonged into the filum terminale. It is lined with a layer of cylindrical 
ciliated cells or epithelium. This canal, though minute, is an object of 
considerable interest as a typical part of the structure of the cord, it being 
the permanent remains of the cavity of the cylinder formed by the spinal 
cord at the earliest period of its development. It is more distinctly seen 



MINUTE STRUCTURE OF THE CORD. 



509 



iu fishes, reptiles, and birds than in mammals. In the young human subject 
it is always present, but, according to the observation of Lock hart Clarke 
and Kolliker, it sometimes disappears in the adult. 

Minute Structure of the Spinal Cord. The substance of the spinal cord consists of a 
large proportion of nervous substance, supported in a delicate framework of connective 
tissue and numerous minute blood-vessels. The white matter presents nerve-fibres, 
but is destitute of nerve-cells the grey matter contains both elements. The fibres 
of the white substance are in greatest part longitudinal; the principal exceptions 
being those contained in the commissure, and in the roots of the nerves. The longi- 
tudinal fibres are finer in the posterior columns and posterior parts of the lateral 
columns than in other parts, and the deepest fibres are smaller than those placed more 
superficially. (Kolliker.) The fibres of the grey substance are for the most part not 
more than one half the diameter of their continuations in the white substance, and in 
the nerve-roots, but among them there are a few of larger size. They are very 
various in their direction, and, in great part at least, are connected with the roots of 
the nerves. 



Fig. 345. TRANSVERSE Fig. 345. 

SECTION OP HALF THE 
SPINAL MARROW IN 
THE LUMBAR EN- 
LARGEMENT, f 

This is a semidia- 
grammatic representa- 
tion taken from a pre- 
pared specimen, and 
founded in part on the 
statements of Lockhart 
Clarke and of Kolliker. 

1, anterior median 
fissure ; 2, posterior 
median fissure ; 3, cen- 
tral canal lined with 
epithelium ; 4, posterior 
commissure ; 5, anterior 
commissure ; 6, posterior 
column ; 7, lateral co- 
lumn ; 8, anterior co- 
lumn ; (at each of these 
places and throughout 
the white substance the 
trabecular prolongations 
of the pia mater are 
shown ; ) 9, posterior 
roots of the spinal nerve 
entering in one principal 
bundle; 10, anterior 
roots entering in four 
spreading bundles of 
fibres ; a, a, caput cornu 
posterioris with large 

and small cells, and above them the gelatinous substance ; b, in the cervix cornu, decus- 
sating fibres from the nerve roots and posterior commissure ; c, posterior vesicular 
columns (of Clarke) ; d, fibres running transversely from the posterior commissure into 
the lateral columns : near d, the lateral group of cells ; e, e, fibres of the anterior 
roots entering the anterior cornu, and passing through among the radiating cells, but 
not joining their processes; e', fibres from the anterior roots which decussate in the 
anterior column ; e", external fibres from the roots running round the outside of the 
anterior grey cornu towards the lateral columns ; f, fibres from the posterior commissure 
and from the posterior cornu running towards the anterior. Three groups of cells are seen 
in the anterior column ; of these the anterior are external and internal, the posterior are 
chiefly external or lateral. 




510 



THE SPIXAL CORD. 



The nerve-cells of the grey matter are of two kinds. Firstly, there are very large 
branched cells, from ^ to ^ of an inch in size, containing nuclei and pigment ; 
secondly, there are smaller cells, ranging from ^^ to ^ of an inch, but the majority 
are from -^^ to ~ of an inch in size. 

The smaller cells occur scattered throughout the whole of the grey matter ; the 
larger cells, on the contrary, are collected into groups. In the posterior cornua the 
large cells are almost entirely collected into a compact group, the posterior vesicular 
column of Clarke (the core of Stilling), which occupies the inner half of the cervix of 
the posterior cornu. This vesicular column is in intimate connection with the 
posterior roots of the nerves ; it may be traced continuously from near the lower 
extremity of the spinal cord to the middle of the cervical enlargement, where it 
terminates ; and it increases in size in both the lumbar and cervical enlargements. 
In the anterior cornu the large cells occur in greater number than in the posterior 
cornu, and are of somewhat greater size ; and they are principally placed at its forepart, 
and arranged in an inner and an outer group. There is likewise described by Clarke a 
small group of cells, collected in a tractus intermedio-lateralis, and forming a projection 
of the grey matter opposite the junction of the anterior and posterior cornua. This 
lateral vesicular column extends from the upper part of the lumbar to the lower part 
of the cervical enlargement ; and it may be said to reappear at the upper extremity 
of the cord, where it is traversed by the roots of the spinal accessory nerve, and is 
continued up into the medulla oblongata. 

Fig. 346. 




Fig. 346. A SMALL PORTION OF A TRANSVERSE SECTION OP THE HUMAN SPINAL CORD 

NEAR THE SURFACE AT THE ENTRANCE OP A BUNDLE OF THE ANTERIOR ROOTS. ^ 

This figure, which is somewhat diagrammatic, is intended to show the relation to the 
nervous substance of the pia-matral sheath of the cord and the processes of connective 
tissue prolonged from it between the longitudinal and other nerve fibres, a, a, the 
primitive filaments of a bundle of the anterior roots, the medullary sheaths not repre- 
sented ; b, b, transverse sections of part of the anterior columns of the cord in which the 
dark points are the primitive filaments, and the circles represent the neurilemmal tube 
enclosing the medullary substance : in these parts the connective tissue is not represented, 
and many of the smallest nerve-fibres have also, for the sake of clearness, been omitted ; 
c, the pia-matral covering of the cord ; d, one of the compartments of the anterior 
column enclosed by septa of connective tissue prolonged from the pia mater, and exhibit- 
ing the fine frame-work of connective tissue extending through among the nerve-fibres, 
which last have been omitted : there are also indicated among the trabeculse minute 
nuclei of connective tissue. 

Connective tissue takes part in the structure of the cord to a very considerable 
extent. It forms a complete covering surrounding the white substance. In the 
inner margin also of the posterior columns, one on each side of the posterior fissure, 
two wedge-shaped bands (the bands of Goll) have been distinguished, in which the 



MINUTE STRUCTURE OF THE CORD. 



511 



connective tissue is remarkably abundant, and the nerve-fibres particularly small. 
The connective tissue forms also a reticulum (processus reticularis), in which the 
longitudinal nerve-fibres are imbedded. In the grey matter the connective tissue is 
still more abundant, more especially in the immediate neighbourhood of the central 
canal. Much discussion has taken place as to whether the smallest cells already 
described are really nervous or belong to the connective tissue. In the present 
imperfect state of knowledge of the development of nervous elements, it might be 
rash to express a decided opinion on this point ; but it may be stated that, independently 
of these, nuclei are figured by Kolliker in the reticulum, and also cells containing 
numerous and dividing nuclei in the neighbourhood of the central canal. 

Origin of the spinal nerves. The anterior and posterior roots of the spinal nerves 
are attached along the sides of the cord in or near the anterior and posterior lateral 
grooves, and opposite to the corresponding cornua of the grey matter ; the posterior 
roots in a straight line, and the anterior roots scattered somewhat irregularly upon 
the surface (Fig. 345). 

The fibres of the anterior roots may be traced into and through the anterior 
cornua. They then diverge in different directions. The innermost fibres, after 
passing through among the cells in the inner group of the anterior cornu, cross in the 
white commissure to the anterior column of the opposite side. Many fibres pass 
backwards in the substance of the anterior cornu, where some of them would appear 
to form connection with fibres proceeding from other parts of the cord, and others to 
spread obliquely upwards and downwards ; while those which are most external 
passing through the outer group of cells, reach the lateral column. 



Fig. 347. A SMALL FOR- Fig. 347. 

TION OF A TRANSVERSE 
SECTION OP THE SPINAL 
CORD AT THE PLACE 
WHERE TWO BUNDLES OP 
THE FIBRES OF THE 
ANTERIOR ROOTS PASS 
INTO THE GREY SUB- 
STANCE. ^P 

This figure may be looked 
upon as representing the 
inner ends of the anterior 
roots of the nerves, of 
which the outer part is 
shown in fig. 346. a, a, 
the two bundles of fibres of 
the anterior root passing 
between the compartments 
of longitudinal fibres of the 
cord ; b, b, these fibres 
running backwards through 
the grey substance towards 
the posterior cornua ; c, c', 
those spreading in the anterior cornua on the one side towards the anterior commissure, 
and on the other round the outer side of the anterior cornu ; d, d, portions of three com- 
partments of the anterior columns in which the longitudinal fibres of the cord are shown 
in transverse section ; e, e, large radiated and nucleated cells in the grey substance of the 
anterior cornu some with three, others with a greater number of processes emanating 
from them : no direct communication is shown between these processes and the nerve 
fibres of the roots. 

The fibres of the posterior roots on reaching the posterior cornu diverge from each 
other in a curved manner, so as to form in great part the substantia gelatinosa. In 
front of this there may be seen, cut across in transverse sections, a group of these 
fibres which turn longitudinally upwards and downwards, and afterwards pass 
forwards, in part at least, to the anterior cornu, and in part to reach by the posterior 
commissure the posterior and lateral columns of the opposite side. Other fibres of 
the posterior roots pass forwards at once through the grey substance to the anterior 




512 THE SPINAL CORD. 

and lateral columns. Another set of fibres slant principally upwards, but some 
downwards, in the posterior columns, and, interlacing with each other, most probably 
enter the grey matter at different heights. Some are lost to view in the posterior 
white columns, and it is uncertain whether or not they immediately ascend through 
these columns to the brain. 

Much discussion has taken place as to the course of the fibres in the cord, and their 
ultimate destination. It is easily understood that, by the examination of sections difficult 
to prepare, limited in extent, liable to undergo changes in the preparation, and giving 
views confined each to little more than a thin lamina, it is scarcely to be expected that 
the full history of many tortuous fibres can be accurately ascertained. Thus it remains 
still undecided whether any of the fibres of the nerve-roots pass up all the way to 
the brain. Volkmann concluded that none of them reached the brain, arguing from 
measurements of the size of the cord in different regions, that the cord could not 
contain in its upper regions all those nerve-fibres which were traceable to it in the 
lower. Kolliker pointed out the fallacy of this conclusion, in so far as Volkmann 
had not made proper allowance for the diminished size of the fibres as they ascend in 
the cord ; but although Volkmann's argument was thereby invalidated, it appears 
impossible to prove by microscopic observations that fibres of nerve-roots traced into 
the grey matter, and observed to emerge into the white matter, do not again re-enter 
the grey and terminate there. (Lockhart Clarke, Phil. Trans., 1851,1853, 1859; 
Stilling, Neue Unters. u. d. Bau des Ruckenmarks, 1856, 1857; Lenhossec, Neue 
Unters. u. d. Bau d. cent. Nervensystems, Vienna, 1855 ; F. Goll, Beitrage z. feineren 
Bau d. Ruckenmarks, Zurich, 1860. For a full account of the whole subject, see 
Kolliker's Handbucb der Gewebelehre des Menschen, 4th ed., 1863). 

It is also undetermined in what relation the nerve-fibres and branched or multipolar 
cells of the cord stand to each other. Most are inclined to believe that the radiating 
prolongations of the cells are in actual con tinuity with the axial filaments of nerve-fibres, 
whether proceeding from nerve-roots or from different parts of the cord itself; and 
the direct observation of such continuity has been affirmed by some, as by Schroeder 
Van der Kolk. But it is still considered by observers who have given most careful 
attention to this investigation that, although such continuity may be regarded as of 
the greatest probability, and, although it may be considered as proved in some other 
parts of the nervous system, especially in the lower animals, the actual passage of 
nerve-fibres into the processes of nerve-cells has not been proved as the result of 
actual observation in the spinal cord of man or of mammals. 

Results of Experiments. Seeing the imperfect nature of the knowledge of the 
minute structure of the spinal cord as obtained from microscopic observations, it 
may be proper to give here a short account of the more important results of 
physiological experiments as to the course of the transmission of sensory impressions 
and motor influences through it, although it is at present difficult to reconcile them 
with the results of anatomical research. For the most important information upon 
this subject, derived from vivisection, science is indebted to the researches of Brown- 
Se"quard and Schiff. 

When the superior or dorsal * half of the cord is divided in animals, sensation still 
continues in the hind limbs. Sensation likewise continues after division of the 
inferior half of the cord, and even after the superior and inferior parts of the cord 
have been divided at different levels in such a manner that the hinder extremity of 
the cord may be supposed to communicate with the brain by means of the central grey 
matter only. But sensation is abolished by piercing the interior of the cord with an 
instrument, and so moving it as to divide as much as possible the grey matter without 
injuring the white matter. Moreover, section of the cord and irritation of the cut 
surfaces produce no pain, provided that the plane of section be sufficiently removed 
from the origins of nerves, as may be accomplished in the cervical region ; but in the 
neighbourhood of nerve-roots there is great sensibility. From all these circumstances 
it appears probable that the sensory fibres, viz., those of the posterior roots, pass 
quickly into the grey substance, and that the grey substance conducts sensory 
impressions upwards. Moreover, the circumstance that the posterior as well as the 
anterior surfaces of transverse sections made near the nerve-roots are sensitive seems 

* The student is reminded that "superior" applied to animals corresponds to 
" posterior" applied to the human subject. 



THE ENCEPHALON. 513 

to be accounted for by the curving of the nerve-roots both toward and away from the 
brain. By similar experiments it is made probable that motor impressions likewise 
travel chiefly in the grey matter of the cord. 

Section of one lateral half of the cord is followed by loss of sensation in the opposite 
hind limb, and of motion in the limb of the side operated on : and a prolonged 
mesial incision produces loss of sensation in both hind limbs, without paralysis 
of motion. But in the medulla oblongata, above the decussation of the anterior 
pyramids, section of one side produces loss of both sensation and motion on the 
opposite side. From these circumstances it appears probable that the sensory fibres, 
viz., those of the posterior roots, decussate in the commissure ot the spinal cord, 
while the motor fibres, those derived from the anterior roots, cross chiefly at the 
decussation of the anterior pyramids of the medulla oblongata. (For further details, 
see Brown-Sequard, " Central Nervous System," 1860; also for a succinct account of 
the subject and for bibliography, J. Be"clard, " Physiologic Humaine," 4th ed., 1862 ; 
" Carpenter's Human Physiology/' 6th edit., 1865.) 



B. THE ENCEPHALON. 

The encephalon admits of being conveniently divided into the medulla 
oblougata, the cerebellum with the pons Varolii, and the cerebrum. 

Fig. 348. 




Fig. 348. PLAN IN OUTLINE OF THE ENCEPHA.LON, AS SEEN FROM THE RIGHT SIDE. J 

The parts are represented as separated from one another somewhat more than natural 
so as to show their connections. A, cerebrum ; /, g, h, its anterior middle and posterior 
lobes; e, fissure of Sylvius; B, cerebellum; C, pons Varolii; D, medulla oblongata; 
a, peduncles of the cerebrum ; b, c, d, superior middle, and inferior peduncles of the 
cerebellum ; the parts marked a, b, c, C, form the isthmus encephali. 

The medulla ollongata is the part continuous with the spinal cord : it 
rests on the basilar process of the occipital bone, and on its superior or 
dorsal surface presents a groove continuous with the central canal of the 
spinal cord. 

The cerebellum occupies the posterior fossa of the cranium. By the 
mesial part of its anterior and inferior surface, it forms the roof of a space, 



5H THE MEDULLA OBLONGATA. 

the floor of which is the grooved posterior surface of the medulla oblongata, 
and which is named the fourth ventricle of the brain. Oil each side of 
this, the cerebellum is connected with the medulla oblongata and cerebrum, 
and also receives the fibres of the pons Parolii, which is a commissure 
passing beneath and between the fibres which extend upwards from the 
medulla oblongata, so as to unite the two lobes of the cerebellum. 

The cerebrum includes all the remaining and much the largest part of the 
encephalon. It is united with the parts below by a comparatively narrow 
and constricted portion or isthmus, part of which, forming the crura cerebri, 
descends into the pons Varolii, and through it is continued into the me- 
dulla oblongata, whilst another part joins the cerebellum. Situated on the 
fibres which extend up from the constricted part, are a series of eminences, 
named, from behind forwards, the corpora quadrigemina, optic thalami, and 
corpora striata ; and springing from the front and outer side of the corpora 
striata are the large convoluted cerebral hemispheres, which expand from 
this place in all directions, concealing the eminences named, and occupying 
the vault of the cranium, the anterior and middle cranial fossse, and the 
superior fossse of the occipital bone. The cerebral hemispheres are united 
together by commissures ; by means of which there is enclosed a cavity, 
which is subdivided into various ventricles, viz., the two lateral, the third, 
and the fifth. 

THE MEDULLA OBLONGATA. 

The medulla ollongata is bounded above by the lower border of the pons 
Varolii, whilst it is continuous below with the spinal cord, on a level with 
the upper border of the atlas, at a point which corresponds with the lower 
extremity of the anterior pyramids, to be presently described. It inclines 
obliquely downwards and backwards ; its anterior surface rests in the 
basilar groove, whilst its posterior surface is received into the fossa 
named the vallecula, between the hemispheres of the cerebellum, and 
there forms the floor of the fourth ventricle. To its sides several large 
nerves are attached. 

The term medulla oblongata, as employed by Willis, by Yieussens, and by those 
who directly followed them, included the crura cerebri and pons Varolii, as well as 
that part between the pons and the foramen magnum, to which, by Haller first, and 
by most subsequent writers, this term has been restricted. 

It is of a pyramidal form, having its broad extremity directed upwards : 
it is expanded laterally at its upper part : its length from the pons to the 
lower extremity of the pyramids is about an inch and a quarter ; its 
greatest breadth is nearly an inch ; and its thickness, from before back- 
wards, is about three-quarters of an inch. 

The anterior and posterior mesial fissures which partially divide the spinal 
cord are continued up into the medulla oblongata. The anterior fissure 
terminates immediately below the pons in a recess, the foramen ccecum of 
Vicq d'Azyr ; the posterior fissure is continued upwards into the floor of the 
fourth ventricle, where it opens and expands in a superficial furrow, and is 
gradually lost. 

In other respects an entirely different arrangement of the parts prevails 
from that in the cord. The surface of each half of the medulla presents 
four eminences or columns, which are met with in the following order, 
from before backwards, viz. : the anterior pyramids, the olivary bodies, the 
restiform bodies, and the posterior pyramids. 



COLUMNS OF THE MEDULLA OBLOXGATA. 



515 



The anterior pyramids are two bundles of white substance, placed one on 
either side of the anterior fissure, and marked off from the olivary body 
externally by a slight depression. They become broader and more pro- 
minent as they ascend towards the pons Varolii. At their upper end they 
are constricted, and thus enter the substance of the pons, through which 
their fibres may be traced into the peduncles of the brain. 



Fig. 349. 




Fig. 349. VIEW OP THE ANTERIOR SURFACE 
OF THE PONS VAROLII AND MEDULLA 
OBLONGATA. 

a, a, anterior pyramids ; 6, their decussation ; 
c, c, olivary bodies ; d, d, restiforra bodies ; e, 
arciform fibres ; /, fibres described by Solly as 
passing from the anterior column of the cord to 
the cerebellum ; g t anterior column of the 
spinal cord ; h, lateral column; p, pons Varolii; 
i, its upper fibres ; 5, 5, roots of the fifth pair 
of nerves. 



In the lower part, a portion of each 
pyramid, arranged in several bundles, 
which interlace with the corresponding 
bundles of the other pyramid, passes 
downwards across the fissure to the oppo- 
site side. This decussation of the pyra- 
mids is not complete, but affects much 
the greater part of the innermost fibres. 
When traced from below, it is found 
that the whole or a great part of the 
decussating fibres come forward from the 

deep portion of the lateral columns of the cord, and advance to the surface 
between the diverging anterior columns, which are thus thrown aside. 
(Rosenthal, " Beitrag zur Encephalotomie," 1815.) 

The outer smaller portion of each pyramid does not decussate ; it consists 
of fibres, derived from the anterior column of the cord : these ascend, and 
are joined by the decussating portion from the opposite side. Together 
they form a prismatic bundle or column of white fibres, which extends 
deeply into the substance of the medulla, and is triangular in a cross 
section. 

The anterior pyramids contain no grey matter. 

The olivary bodies are two prominent oval masses placed to the outer sida 
of the pyramids, and sunk to a considerable depth in the substance of the 
medulla oblongata, appearing on its surface like two smooth oval eminences. 
They do not reach the pons Yarolii above, being separated from it by a 
deep depression ; nor do they extend so far in a downward direction as the 
pyramids, being considerably shorter than those bodies. 

The olivary bodies consist externally of white substance, of which the 
fibres chiefly run longitudinally ; and internally of a grey nucleus, named 
corpus dentatum or ciliare, or olivary nucleus. 

The olivary nucleus appears, on making a section, whether horizontal or 
vertical, through the middle, to present the form of a zig-zag line of a light 
yellowish colour, circumscribing a whitish substance within, and interrupted 
towards the centre of the medulla. It is arranged in the form of a capsule, 
which is open at its upper and inner part, and has its sides corrugated or 



516 



THE MEDULLA OBLOXGATA. 



plicated, so as to give the indented appearance to a section. This capsule is, 
moreover, surrounded with white matter externally, and through its open part 
white fibres pass into or issue from its interior, and connect it with other 
parts of the brain. The external fibres of the anterior columns of the cord, 
which at the decussation of the pyramids are thrown outwards, are con- 
tinued upwards, on the surface of the medulla oblongata, and then pass 
partly on the outside of and partly beneath the olivary bodies being joined 
in their further progress by the fibres issuing from the olivary nucleus. To 
these fibres the term olivary fasciculus has been applied. 

The restiform bodies, placed behind and to the outer side of the olivary 
bodies, are two lateral rounded eminences or columns directly continuous with 
the posterior, and with part of the antero-lateral columns of the cord ; they 
diverge slightly as they ascend, and thus occasion the greater width of the 

Fig. 350. Fig. 350. VIEW OF THE POSTERIOR SURFACE OF 

THE PONS VAROLII, CORPORA QUADRIGEMINA, 
AND MEDULLA OBLONGATA. 

The peduncles of tbe cerebellum are cut short 
at the side, a, a, the upper pair of corpora quadri- 
gemina ; 6, b, the inferior ;/,/, superior peduncles 
of the cerebellum ; c, eminence connected with 
the nucleus of the hypoglossal nerve; e, that of 
the glosso-pharyngeal nerve ; i, that of the vagus 
nerve ; d, d, restiform bodies ; p, p, posterior 
pyramids ; v, v, groove in the middle of the fourth 
ventricle ; v, calamus scriptorius, and eminence 
connected with the spinal accessory nerve ; 7, 7, 
roots of the auditory nerves. (See also Fig. 357, 
at p. 525.) 

medulla at its upper part. Each of them 
passes into the corresponding hemisphere 
of the cerebellum, and constitutes its 
inferior peduncle. At first they are in 
contact with the small tracts of the 
medulla, named the posterior pyramids ; 
but higher up they become free and pro- 
minent, and assist in forming the lateral boundaries of the fourth ventricle. 
There is a considerable portion of grey matter in their interior. 

By far the larger portion of the white substance of the restiform body 
consists of longitudinal fibres, which include all those belonging to the 
posterior column of the cord except the fasciculus gracilis, some derived 
from the lateral column, and also a small band from the anterior column. 
This last-named band runs obliquely below the olivary body, and, as was 
shown by Solly, connects the anterior column with the cerebellum. 

The part of the posterior column of the cord which belongs to the resti- 
form body of the medulla, is named fasciculus cuneatus. 

The posterior pyramids (fasciculi graciles) of the medulla oblongata, the 
smallest of the four pairs of columns into which it is divided, are situated 
one on each side of the posterior median fissure. They consist entirely of 
white fibres, and are continuous with the posterior slender tracts of the 
cord. They increase in size as they ascend till they reach the point where 
the medulla opens out to form the floor of the fourth ventricle ; and there, 
diverging from one another, they have the appearance of tapering and 
become closely applied to the restiform bodies. Their fibres quit these 
bodies, however, and pass up to the cerebrum. 




STEUCTUHE OF THE MEDULLA OBLONGATA. 517 

The floor of the fourth ventricle, or space between the medulla and cere- 
bellum, is formed by that portion of the back of the medulla oblongata 
which is situated above the divergence of the posterior pyramids. Upon it, 
the central grey matter of the medulla oblongata, is, as it were, opened out 
to view. It is marked by a median furrow, ending inferiorly in the calamus 
scri2Jtorius, and at its lower end is a tubular recess, passing down the centre 
of the medulla for a few lines. This, which has been sometimes named the 
ventricle of Arantius, is the upper expanded portion of the central canal of 
the spinal cord. 

In the upper part of the floor of the fourth ventricle are two longitudinal 
eminences, one on each side of the middle furrow, greyish below, but 
appearing white higher up. These are formed by two bundles of white 
fibres, mixed with much grey matter, the fasciculi teretes of some authors, 
les faisceaux innomines of Cruveilhier. They seem to be derived from part 
of the lateral columns of the cord ; Cruveilhier believes, however, that they 
arise from the grey matter at the lower end of the medulla oblongata. 

Surmounting the free inner margin of the restiform body and posterior 
pyramid is a thin lamina, the lifjula (smaller pous of Meckel) occupying the 
angle between the cerebellum and the restiform body, and stretching towards 
its fellow of the opposite side. It derives a certain interest from indicating 
how the cylinder, which is closed in the spinal cord, might be completed in 
this region of the medulla oblongata by the union of the opposite margins. 

Crossing the grey matter in the floor of the fourth ventricle several 
transverse white lines, or stride, are usually observed, passing outwards from 
the median fissure, and round the sides of the restiform bodies. Some of 
these white strise form part of the roots of the auditory nerves, a few run 
slantingly upwards and outwards on the floor of the ventricle, whilst others 
again embrace the corresponding half of the medulla oblongata. These 
transverse lines are sometimes wanting, in which case the white fibres on 
which they depend probably exist at some depth below the surface. 

Santorini, and subsequently Kolando, described a set of superficial white fibres on 
the fore part and sides of the medulla oblongata, crossing over it below the olivary 
bodies, fibrce vel processus arciformes. They belong to a system of white fibres which 
pass transversely or horizontally outwards, and are probably continuous with the 
septal fibres about to be noticed. Sometimes the greater part of the pyramidal and 
olivary bodies is covered by a thin stratum of these transverse fibres, which appear to 
issue from the anterior median fissure ; but, most commonly, these superficial fibres 
are found only at the lower extremity of the olive, as the arciform fibres already 
mentioned. 

Besides the superficial transverse fibres now referred to, the medulla oblongata 
presents other horizontal fibres in its interior, some of them disposed in a mesial 
raphe or septum, and numerous others proceeding from that septum transversely 
outwards. Of these last, the majority, passing through the olivary bodies, and in part 
the pyramids, enter the corpus dentatum and form the whole of its white substance ; 
and these fibres, then passing radiately through the grey capsule, turn backwards to 
the fasciculus cuneatus and lateralis, those of them which pierce the anterior wall of 
the capsule arching round it to reach their destination. Other fibres pass behind the 
olivary into the restiform bodies, and seem to terminate in the grey substance of the 
floor of the fourth ventricle. (See Kolliker's Handbuch der Gewebelehre, 1863, 
p. 316.) 

A small band of fibres is represented by Eeichert as passing obliquely downwards 
and backwards from the side of the pons Varolii, descending between the auditory 
and facial nerves, and crossing over the upper end of the posterior pyramids. He 
names it the ala pontis. It probably is part of the ligula. (Keichert, Bau des 
Menschl. Gehirns, part 1st, plate I., 1859.) 



518 



THE MEDULLA OBLONGATA. 



Course of fibres from the spinal cord upwards through the medulla 
oblongata. Assuming, for convenience of description, the existence of three 
white columns of the cord, these are disposed as follows. 

1. The posterior column, with the exception of the fasciculus gracilis, is 
distinguished by the name of processus cuneatus and enters into the forma- 
tion of the restifonn body, which ascends to the cerebellum. The fasciculus 
gracilis ascends to the cerebrum. 

2. The lateral column ascends towards the base of the olivary body, and 
is disposed of in three ways ; (1,) some of its fibres from the surface and 
deep part join the restiform body and proceed with it to the cerebellum ; 
(2,) a larger number, passing obliquely inwards, then come forwards between 
the anterior columns, and crossing the median plane appear as the fibres of 
decussation, and form the chief part of the opposite anterior pyramid ; (3,) 
the remaining fibres pass up to the cerebrum, as the fasciculi teretes 



Fig. 351. Fig. 351. DIAGRAMMATIC REPRESENTA- 

TION OP THE PASSAGE OF THE COLUMNS 
OP THE MEDULLA OBLONGATA UPWARDS 
AND DOWNWARDS. 

A, the specimen, which, is seen from 
before, includes the medulla oblongata and 
the pons Varolii, with a small portion of 
the spinal marrow. The left lateral column 
(that to the reader's right) has been lifted 
out of its place to the side, and the ante- 
rior and posterior columns of that side 
remain undisturbed : the right anterior and 
posterior columns have been removed, and 
the lateral column remains in its place. 
The upper part of the right pyramid is 
removed. The transverse fibres of the pons 
Varolii have been divided in circumscribed 
portions to different depths corresponding 
with the several places of passage of the 
columns of the medulla. 

P, pons Varolii, part of the anterior sur- 
face, where it has been left entire ; p, the 
right and left pyramids, the upper part of 
the right has been cut away ; p', the fibres 
of the left pyramid as they ascend through 
the poris exposed by the removal of the 
superficial transverse fibres ; p'', placed on 

the deeper transverse fibres of the pons on the right side, close below the divided fibres 
of the pyramid ; a, left anterior column of the cord, passing upwards into the undecus- 
sated part of the anterior pyramid, and into a', the olivary column ; 0, olivary body ; 
o', the continuation of the olivary column ascending deeply through the pons, and 
exposed by the removal of a small portion of the deeper transverse fibres; o", the 
same fibres divided by a deeper incision on the right side ; I, the right lateral column, 
passing upwards into the following parts, viz., x, the deeper part passing by decussation 
into the left pyramid ; r, the part passing into the restiform body ; ft, the part ascending 
in the back of the fourth ventricle as fasciculus teres ; to the outer side of this are seen 
the ascending fibres of the posterior pyramid ; I', the left lateral column drawn aside 
from its place in the spinal cord ; the fasciculus teres, ft, and the part to the restiform 
body, r, cut short ; x , the deeper part passing by decussation into the right pyramid ; 
r', the part of the restiform body derived from the anterior column of the spinal cord ; 
pc, the posterior column of the left side exposed by the removal of the lateral column, 
and shown ascending to the restiform body as fasciculus cuneatus, fc : on the right side 
the posterior column being removed, fc, points to this fasciculus cuneatus cut short 
below. 

B, explanatory outline of the section of the spinal cord, a, anterior columns ; p, 
posterior; I, lateral. 




MINUTE STRUCTURE OF THE MEDULLA OBLOXGATA. 519 

(faisceaux innomine's), appearing on the back of the pons Varolii, in the 
upper part of the floor of the fourth ventricle. 

3. The anterior columns having reached the apex of the anterior pyramids, 
are thrust aside from their median position by the decussating fibres derived 
from the lateral columns, and are then distributed in three divisions. (1,) A 
very small division, ascends obliquely backwards beneath the olive, and joins 
the restiform body (Solly). (2,) Another division passes directly upwards, 
its fibres embracing the olivary nucleus, above which they are again collected 
together, and are joined by other fibres arising from the nucleus, so as to 
form the olivary fasciculus ; this ascends through the pons and at the side 
of the cerebral peduncle under the name of the fillet, and reaches the corpora 
quadrigemina and the cerebral hemispheres. (3,) The remaining division of 
the anterior column ascends into the anterior pyramid, forming its outer 
part. The anterior pyramids therefore are composed of fibres from the 
lateral and anterior columns, and are continued up through the pons into 
the peduncles of the cerebrum. 

It is to be remembered, however, that the separation between these 
different tracts of white fibres cannot be clearly followed out through the 
whole structure of the medulla oblongata, but that they are more or less 
blended with one another. 

Grey matter of the medulla oblongata followed upwards from the cord. The 
central canal of the spinal cord, together with the grey matter which surrounds it, 
approaches nearer and nearer to the back of the medulla oblongata as it ascends, until 
it terminates in the calamus scriptorius. 

The anterior pyramids are free from grey matter in their interior, and are separated 
from the rest of the medulla by strong septa of connective tissue, and from one 
another by a raplie, which extends back to the grey matter surrounding the central 
canal, and which contains mesial horizontal fibres, named septal. The posterior 
cornua of grey matter in the lower part of the medulla oblongata extend transversely 
outwards from the central canal, and higher up stretch outwards and forwards to the 
surface. The substantia gelatinosa is swollen out into a mass which appears circular 
in a transverse section, and is named the grey tubercle of Rolando. The anterior 
cornua, together with the intermedio-lateral tract, which had re-appeared at the upper 
end of the cord, vanish in the form of elongated radiating streaks ; and between them 
and the anterior pyramids appear the olivary nuclei, unconnected with the system of 
grey matter prolonged from the spinal cord. Behind the posterior cornua two new 
cornua make their appearance one extending into the processus cuneatus and the 
other into the posterior pyramid, and both of them increasing in size as the posterior 
pyramids increase. In the neighbourhood from which these and the posterior cornua 
spring there is seen in transverse sections a limited bundle of white fibres, the round 
fascicle of Stilling. In the upper part of the medulla oblongata the grey matter is 
principally spread out on the floor of the fourth ventricle. (Reichert, op. cit., part 
2nd, plates I. and II.) 

According to the observations of Stilling, part of the grey matter at the back 
of the medulla forms special deposits or nuclei, which are connected with the roots 
of the spinal accessory vagus, glosso-pharyngeal, and hypoglossal nerves. Of these 
nuclei, the first or lowest is concealed in the substance of the medulla; whilst 
those which are situated higher up gradually appear in the floor of the fourth 
ventricle as small angular eminences pointing downwards, near the apex of the calamus 
scriptorius. The first nucleus proceeding from below is that for the spinal accessory 
nerve. It reaches some way down in the cord, and is there lost in the intermedio- 
lateral tract. Above this nucleus, and close to the middle of the medulla, is another, 
the second, commencing higher up, and connected with the hypoglossal nerve, the 
roots of which, coming forward between the anterior pyramid and the olivary body, 
appear at the surface in the depression between those parts. Continuing to ascend, 
these two nuclei reach the back of the medulla, and then make their appearance in 
the floor of the fourth ventricle. Higher up, the nucleus for the spinal accessory 



520 



THE MEDULLA OBLONGATA. 



Fig. 352. 



nerve is succeeded by a third in the same line, which is connected with the nervus 
vagus, and is also placed to the outer side of that for the hypoglossus. Further out, 
a fourth nucleus begins to be observed, belonging to the glosso-pharyngeal nerve. 
The last change in the arrangement of these small grey masses consists in the gradual 

narrowing of the nucleus of the par va- 
gum, and the approximation of those for 
the hypoglossal and glosso-pharyngeal 
nerves which were previously separated 
by it. 



Fig. 352. MAGNIFIED VIEWS OF TRANS- 
VERSE SECTIONS OF THE MEDULLA OB- 
LONGATA (after Lockhart Clarke, and 
Reichert). f 

These figures are to be looked upon as in 
part diagrammatic, no attempt having been 
made to represent the natural difference of 
colour in the parts. For the most part, 
however, the grey substance is'indicated by 
the smoother dark shading, and the white 
substance by distinct lines. 

A, represents a section made at the 
lower part of the decussation of the pyra- 
mids; B, one immediately below the 
olivary bodies ; C, one a very short dis- 
tance below the calamus scriptorius ; and 
D, a section in the lower part of the fourth 
ventricle. The references are the following 
in all the four figures : 

p, anterior pyramids ; p', their decussa- 
tion ; 0, olivary bodies ; 0', the radiating 
fibres proceeding from their interior; r, 
restiform bodies and their nucleus ; pp, 
posterior pyramids ; R, raphe ; c, central 
canal and substance surrounding it ; tr, 
grey tubercle of Rolando ; /, anterior 
median fissure ; fp t posterior median 
fissure ; a, arciform fibres ; I, lateral 
column ; Z', larger cells and vesicular tract 
of the lateral column ; CI a, anterior roots 
of the first cervical nerve ; CI p, posterior 
roots ; XII, hypoglossal nerve-roots issuing 
at the side of the pyramid ; XII', its 
nucleus ; XI, XI', spinal accessory nerve 
and its nucleus ; VIII', nucleus of the 
auditory nerve according to Reichert. 

In A and B, the decussation of the pyra- 
mids is represented ; in A, the anterior 
and posterior cornua of the grey matter 
still exist as in the spinal cord ; in B, the 
anterior cornua are much diminished in 
size, the posterior have begun to pass 
outwards, and to be converted into the 
grey tubercles, and the intermediate nuclei 
to make their appearance between them ; 
in C, the central canal is wider and ap- 
proaches the posterior aspect, and the 
olivary body appears between the anterior 
pyramid and the lateral column ; in D, the 
canal is opened up in the fourth ventricle, 
and the various grey nuclei are for the 
most part in the vicinity of its floor. 




C. 



a- 



Langenbeck and Forg maintain that the pail regarded by Stilling as the nucleus 




TEE PONS VAROLII. 521 

for the glosso-pharyngeal nerve is really the place of origin of the greater root of the 
fifth or trigeminal nerve. 

Fig. 353. TRANSVERSE SECTION Fig. 353. 

OF THE MEDULLA OBLONGATA 
(after Stilling). 

The section is made at the level 
of the middle of the olivary bodies]; 
the effect produced by transmitted 
light is brought out on the left- 
hand side of the figure, the half 
to the right being only sketched, 
a, anterior, and p, posterior 
fissure ; b, anterior pyramid ; c, 
olivary body with its corpus 
dentatum shown internally ; d, 
grey tubercle of Rolando in the 
lateral column ; e, the restiform 
body and its nucleus ; /, nucleus 
of the roots of the glosso-pharyn- 
geal nerve ; g, nucleus of the pneumo-gastric nerve ; h, that of the hypoglossal nerve ; 
z, the septum or raphe ; 8, roots of the pneumo-gastric nerve emerging ; 9, roots of the 
hypoglossal nerve. 

THE PONS VAROLII AND CEREBELLUM. 

THE PONS VAROLII or tuber annulare (mesocephalon of Chaussier, nodus 
encepliali of B-au and Sommerring), forms an eminence of transverse fibres 
above and in front of the medulla oblongata, below and behind the crura 
cerebri, and between the lateral lobes of the cerebellum. Its margins are 
arched ; the superior much more so than the inferior : thus, at the sides its 
transverse fibres are much more gathered together, and form at the place 
where it passes into the cerebellum a narrower bundle, which is named the 
middle cms of the cerebellum. In the middle line the pons presents a 
shallow groove in which the basilar artery lies, and is perforated by small 
branches of that artery. 

Although the superficial fibres are transverse in their general direction, 
they are not all parallel to each other. The middle fibres pass directly 
across, the lower set ascend slightly, whilst the superior fibres, which are the 
most curved, descend obliquely to reach the crura cerebelli on each side ; 
and there are also one or more superficial bands of the superior fibres 
which cross obliquely downwards over the middle and lower fibres, and 
completely conceal them at the sides. 

In its internal structure the pons consists of the longitudinal or peduncular 
fibres prolonged upwards from the medulla oblongata, of its own transverse 
or conimissural fibres, through which the longitudinal fibres pass, and of a 
large intermixture of grey matter. Behind the superficial transverse fibres 
are seen the prolonged fibres of the anterior pyramids, which, as they ascend 
through the pons, are widely separated into smaller bundles, intersected by 
other transverse white fibres, which, with those upon the surface, are all 
continued into the cerebellum. 

The alternation of transverse and longitudinal fibres just described extends 
to a considerable depth in the pons, the quantity of transverse fibres greatly 
preponderating ; posteriorly there succeeds a third layer, consisting entirely 
of longitudinal fibres, and comprehending the olivary fasciculi, and the 
fasciculi teretes. 

The median septum or raphe, which exists in the medulla oblongata, is 

M M 



522 THE CEREBELLUM. 

prolonged throughout the whole height of the pons in its back part, but 
becomes indistinct in approaching the front or basilar surface, except towards 
its upper and lower edge, where the superficial fibres of the pons are mani- 
festly continuous in the median line with these septal fibres. Bundles of 
white fibres, belonging to the same system, encircle the crura cerebri at 
their emergence from the upper border of the pons. 

According to Foville, a few fibres from each of the three principal longitudinal 
elements of the medulla turn forwards and become continuous with the transverse 
fibres of the pons ; and, in like manner, one or more small bundles from each of the 
crura cerebri take a similar transverse course. (Foville, op. cit., pi. II., figs. 2 and 3 ; 
pi. III., figs. 5 and 6.) 

THE CEREBELLUM, hinder brain, consists of a body and of three pairs of 
crura or peduncles, by which it is connected with the rest of the eucephalon. 
These crura are named superior, middle, and inferior. 

Fig. 354. Fig. 354. OUTLINE OP THE UPPER 

SURFACE OF THE CEREBELLUM. 

At the upper part of the figure, the 
crura cerebri and parts behind them 
have been cut through and left in con- 
nection with the cerebellum. 

Ill, the third pair of nerves lying 
upon the crura cerebri ; c r, white 
matter or crust of the crura cerebri ; 
In, locus niger ; t, tegmentum contain- 
ing grey matter in the upper part of 
the crura ; a s, aqueduct of Sylvius ; 
q, corpora quadrigemina, the upper 
elevations divided ; s v, superior ver- 
miform process or central folia of the 
middle lobe of the cerebellum ; I q, 
lobulus quadratus ; p s, posterior supe- 
rior lobe; fh, horizontal fissure ; pi, 
posterior inferior lobe; n, the notch 
between the hemispheres. 

The superior peduncles, crura ad cerebrum or processus ad testes, together 
with the valve of Vieusseus, a lamina stretched between them, connect the 
cerebellum with the cerebrum. 

The inferior peduncles, crura ad medullam, are the upper extremities of 
the restiform bodies. 

The middle peduncles, or crura ad pontem, much the largest, are the 
lateral extremities of the transverse fibres of the pons Varolii. They 
connect together the two halves of the cerebellum inferiorly. 

All these peduncles consist of white fibres only ; and they pass into the 
interior of the cerebellum at its fore part. 

The cerebellum is covered with grey cortical substance, rather darker 
than that of the cerebrum. Its greatest diameter is transverse, and 
extends to about three and a half or four inches : its width from before 
backwards is about two or two and a half inches ; and its greatest depth 
is about two inches, but it is much thinner round its outer border. 

It consists of two lateral hemispheres joined together by a median portion 
called the vermiform process, which in the human subject is distinguishable 
only as a small though well-marked part below, named the inferior vermiform 
process, and a mere elevation above, called the superior vermiform process. 
In birds, and in animals lower in the scale, this middle part of the cerebellum 




FORM OF THE CEREBELLUM. 523 

alone exists ; and in most mammals it forms a central lobe very distinct from 
the lateral portions. 

The hemispheres are separated behind by a deep notch. Superiorly, the 
median portion or upper vermiform process, though slightly elevated, is not 
marked off from the hemispheres, so that the general surface of the organ, 
which is here inclined and flattened on each side, is uninterrupted. Below, 
the hemispheres are convex, and are separated by a deep fossa, named the 
vallecula, which is continuous with the notch behind, and in which the 
inferior vermiform process lies concealed in a great measure by the sur- 
rounding parts. Into this hollow the medulla oblongata is received in front, 
and the falx cerebelli behind. 




Fig. 355. INFERIOR SURFACE OF THE CEREBELLUM WITH THE PONS VAROLII AND 
MEDULLA OBLONQATA (from Sappey after Hirschfeld and Leveille.) f 

1, placed in the notch between the cerebellar hemispheres, is below the inferior 
vermiform process ; 2, 2, median depression or vallecula ; 3, 3, 3, the biventral, slender, 
and posterior inferior lobules of the hemisphere ; 4, the amygdala ; 5, flocculus or sub- 
peduncular lobule ; 6, pons Varolii ; 7, its median groove ; 8, middle peduncle of the 
cerebellum ; 9, medulla oblongata ; 10, 11, anterior part of the great horizontal fissure ; 
12, 13, smaller and greater roots of the fifth pair of nerves; 14, sixth pair; 15, facial 
nerve; 16, pars intermedia; 17, auditory nerve; 18, glosso-pharyngeal ; 19, pneuino- 
gastric ; 20, spinal accessory; 21, hypoglossal nerve. 

The cerebellum, at the surface and for some depth, consists of numerous 
nearly parallel laminse or folia, which are composed of grey and white 
matter, and might be compared with the gyri of the cerebrum, but are 
smaller and without convolution. These laminae are separated by slightly - 
curved grooves or sulci of different depths. 

One principal fissure, or sulcus, named the great horizontal fissure, divides 
the cerebellum into an upper and a lower portion. It begins in front at the 
entrance of the middle peduncles, and passes horizontally backwards round 
the outer border of the hemispheres. From this primary fissure, numerous 
others proceed on both the upper and under surfaces, forming nearly parallel 
curves, having their concavities turned forwards, and separating the folia from 
each other. All these furrows do not go entirely round the hemisphere, for 
many of them coalesce with one another ; and some of the smaller furrows 
have even an oblique course between the others. Moreover, on opening the 

M M 2 



624 THE CEREBELLUM. 

larger fissures, many of the folia are seen to lie concealed within them, and 
do not reach the surface of the cerebellum. 

Certain fissures, which are deeper than the rest, and constant in their 
position, have been described as separating the cerebellum into lobes, which 
are named as follows. 

The central lobe, situated on the upper surface, consists of about eight 
folia, immediately adjoining the anterior concave border. The superior and 
anterior lobe, sometimes called quadrate, and the superior and posterior lobe, 
are placed between the central lobe and the great horizontal fissure. On the 
under surface are seen successively the inferior posterior lobe, the slender 
lobe, the biventral lobe, the amygdala, and the subpeduncular lobe or flocculus. 
This last-named lobule, lobule of the pneumo-gastric nerve (Vicq-d'Azyr), 
subpeduncular lobe (Gordon), or flocculus, projects behind and below the 
middle peduncle of the cerebellum. It is connected by a slender pedicle of 
white fibres to the rest of the hemisphere ; but its exposed surface is grey, 
and is subdivided into five or six small laminae. 

Fig. 356. 




Fig. 356. INFERIOR SURFACE OP THE CEREBELLUM WITH THE POSTERIOR MEDULLARY 
VELUM (after Reil and Reichert, and from nature). f 

The medulla oblongata has been in great part removed by a cut passing through it 
near the pons Varolii ; the two amygdaloid lobules have also been removed, and the 
medulla and pons Varolii pulled downwards in order to bring into view the posterior 
medullary velum. 

p s, posterior superior lobe of the cerebellum ; fh, horizontal fissure ; p i, posterior 
inferior lobe ; g, lobulus gracilis ; b i, biventral lobe ; c, placed on the folia which pass 
across between the hemispheres of opposite sides ; p, pyramid ; u, uvula ; n, placed in 
the fourth ventricle immediately below the nodule ; p v, on each side, placed on the cut 
surface where the amygdalae have been removed, points by a line to the posterior medullary 
velum ; v, v, cavity of the fourth ventricle within the borders of the velum and behind 
the inferior cerebellar peduncles; the cavity extends on each side into the pedicle of the 
flocculus, /; m, section of the medulla oblongata, in which the posterior opening of the 
olivary capsules of grey matter is shown ; VI, sixth nerves ; V, roots of the fifth nerves, 
and above them, the facial and auditory roots. 

Within the vallecula, or on its borders, the following parts are seen. 

Commencing from behind, a conical and laminated projection named the 
pyramid, is first met with. In front of that is another smaller projection, 
called the uvula, which is placed between the two rounded lobes at the sides of 
the vallecula, named the amygdala ; these terms having been suggested by 
a comparison with the parts so named in the throat. Between the uvula 
and amygdalse on each side, but concealed from view, is extended a ridge 



CENTRAL LOBE. FOURTH VENTRICLE. 



525 



of grey matter' indented on the surface, and named the furrowed band. 
Still further forward is the anterior pointed termination of the inferior 
vermiform process, named the nodule, which projects into the fourth ven- 
tricle, and has been named the laminated tubercle (Malacarne). On each 
side of the nodule is a thin white lamella of a semilunar form, which is 
attached by its posterior convex border, and is free and concave in front. 
The outer ends of these lamellss are attached to the flocculi, and the inner 
ends to the nodule, and to each other in front of that projection. The two 
lamellae together constitute the posterior medullary velum, which has been 
compared with the valve of Vieussens, the one being attached to the 
superior extremity and the other to the inferior extremity of the middle 
or vermiform portion of the cerebellum. This posterior velum is covered in 
and concealed by the amygdalae, and cannot be properly seen until those 
lobules have been turned aside or removed. 

The fourth ventricle. The space left between the medulla oblongata in 
front and the cerebellum behind, is named the fourth ventricle, or ventricle 
of the cerebellum. 

Fig. 357. VIEW OP THE Fig. 357. 

FLOOR OP THE FOURTH VEN- 
TRICLE WITH THE POSTERIOR 
SURFACE OF THE MEDULLA 
OBLONGATA AND NEIGH- 
BOURING PARTS (from Sappey 
after Hirschfeld and Le- 
veille). 

On the left side the three 
cerebellar peduncles have been 
cut short ; on the right side 
the white substance of the 
cerebellum has been preserved 
in connection with the supe- 
rior and inferior peduncles, 
while the middle one has been 
cut short. 

1, median groove of the 
fourth ventricle with the fas- 
ciculi teretes, one on each 
side; 2, the same groove at 
the place where the white 
striae of the acoustic nerve 
emerge from it to cross the 

floor of the ventricle ; 3, inferior peduncle or restiform body ; 4, posterior pyramid ; 
above this the calamus scriptoriua ; 5, superior peduncle or processus a cerebello ad 
cerebrum ; on the right side the dissection shows the superior and inferior peduncles 
crossing each other as they pass into the white stem of the cerebellum j 6, fillet to the 
side of the crura cerebri ; 7, lateral grooves of the crura cerebri ; 8, corpora quadri- 
gemina. 




The cavity of this ventricle is of a flat rhomboidal shape, being contracted 
above and below, and widest across its middle part. The anterior extremity 
of the inferior vermiform process projects into it from behind, and higher 
up it is covered by the Vieussenian valve. It is bounded laterally by the 
superior peduncles, and by the line of union of the medulla oblongata and 
the cerebellum. The upper end of the ventricle is continuous with the 
Sylvian aqueduct or passage (iter) leading up to the third ventricle. 

The anterior surface or floor of the fourth ventricle is formed by the back 
of the medulla oblongata and pons Varolii. It is shaped like a lozenge, 



526 THE CEREBELLUM. 

truncated at its upper part. Below, it is bounded by the diverging posterior 
pyramids and restiform bodies surmounted by the ligula. It has already 
been sufficiently described in connection with the medulla oblongata. 

The lining membrane of the ventricle is continuous with that of the 
ventricles in the interior of the cerebrum, through the aqueduct of Sylvius, 
in which situation it is marked by delicate rugse, oblique or longitudinal in 
direction. At the sides it is reflected from the medulla to the cerebellum, 
and extends for a considerable distance outwards between the flocculus and 
the seventh and eighth nerves. At the lower end of the ventricle, there is, 
as was ascertained by Magendie, a narrow orifice in the membrane by which 
the cavity communicates with the subarachnoid space. 

Projecting into the fourth ventricle at each side, and passing from the 
point of the inferior vermiform process outwards and upwards to the outer 
border of the restiform bodies, are two small vascular processes, which have 
been named the choroid plexuses of the fourth ventricle. 



Fig. 358. Fig. 358. OUTLINE SKETCH OP A VER- 

TICAL SECTION OF THE CEREBELLUM TO 
SHOW THE CORPUS DENTATUM IN ITS 
MEDULLARY STEM. 

The section has been carried through the 
left lateral part of the pons so as to divide 
the superior peduncle and pass nearly 
through the middle of the left cerebellar 
hemisphere. The olivary body has also 
been divided longitudinally so as to expose 
in section its corpus dentatum. 

cr, crus cerebri ; /, fillet ; q, corpora 
quadrigemina ; sp, superior peduncle of 
the cerebellum divided; m p, middle 
peduncle or lateral part of the pons Varolii, with fibres passing from it into the white 
stem ; av, continuation of the white stem radiating towards the arbor vitse of the folia ; 
cd, corpus dentatum ; o, olivary body with its corpus dentatum; p, anterior pyramid. 

Internal structure of the cerebellum. The central part is composed of 
white matter, which sends out spreading and gradually thinning layers into 
the interior of all the laminse, larger and smaller, of the grey substance 
which form a continuous covering on the surface. In consequence of this 
arrangement of the white and grey substances, sections of the cerebellum 
crossing the laminae, and dividing the grey and white substance together, 
present a beautifully foliated or arborescent appearance, named arbor vitce. 
This appearance is seen in any vertical section, but it is most perfect in that 
which passes through the median plane, where the relative quantity of the 
central white matter is small. The foliations are arranged somewhat pin- 
nately, the section of each primary lamina having those of secondary laminse 
clustered round it like leaflets 011 a stalk. 

In the lateral hemispheres, where the peduncles enter, the white matter 
is more abundant ; and, if a section be made through either hemisphere half 
way between its centre and the middle of the vermiform process, it will 
display a nucleus of grey matter, which is named the corpus dentatum of the 
cerebellum. This structure, very similar to that already described in the 
olivary body of the medulla oblongata, presents the appearance of a 
waved line of compact yellowish brown matter, surrounded by white sub- 
stance and containing whitish matter within. This line is interrupted at 





INTERNAL STRUCTURE OF CEREBELLUM. 527 

its upper and inner part. In whatever direction the section is carried 
through the corpus dentatum, this waved line is seen, so that the dentate 
body may be described as consisting of a plicated pouch or capsule of grey 
substance open at one part and inclosing white matter in its interior, 
like the corpus dentatum of the olivary body. White fibres may be traced 
from it to the superior peduncles of the cerebellum and to the valve of 
Vieussens. 

Fig. 359. VIEW OF A DISSECTION 
OF THE FIBRES OF THE MEDULLA 
OB LONG AT A AND PoNS VAROLII 
(from Arnold). 

6, the anterior pyramid ; &', its 
fibres traced upwards through, the 
pons Varolii ; c, olivary column ; d, 
olivary body ; m, superficial trans- 
verse fibres of the pons on its left 
side ; m', the deeper transverse 
fibres of the right side; m", the 
prolongation of these fibres as mid- 
dle peduncle of the cerebellum ; 
p, q, their continuation into the 
laminse and folia of the cerebellum ; 
n, inferior peduncle; x, the decus- 
sating part of the left lateral 
column crossing to the right ante- 
rior pyramid. 

The fibres in the primary lamelke can be traced continuously from the peduncles of 
the cerebellum. Upon these central plates are laid other collateral lamellae, which 
are not connected with the fibres proceeding from the middle of the cerebellum, but 
merely pass from one folium to another. 

The grey matter is not uniform throughout its whole thickness, but is composed of 
two or more layers differing in colour and other characters ; resembling, in this 
respect, the cortical substance of the posterior convolutions of the cerebrum. 

The fibres composing the peduncles of the cerebellum are arranged in its interior 
in the following manner. The middle peduncles, which are the most superficial, enter 
the lateral parts of the cerebellum ; they may be traced into the folia of those parts, 
and form a large share of each hemisphere. The inferior peduncles pass upwards 
into the middle part of the cerebellum, in the folia of which they are distributed, 
especially in those of the upper surface. The superior peduncles, which are placed 
nearest to the middle line, are principally connected with the folia of the inferior 
vermiform process ; but a considerable number of them pass into or issue from the 
grey capsule of the corpus dentatum which has been already described. 

A very different account from, that which has generally been received of the course 
and relations of the tracts of nervous substance of the cerebellum has recently been 
put forward by Luys, and deserves mention in this place. According to the statement 
of this author, all the fibres of the cerebellar peduncles arise from the interior of the 
corpora dentata ; the cells of those centres receive externally fibres from the laminated 
periphery of the cerebellum, and internally give origin to the peduncular fibres ; the 
fibres of the inferior peduncles of opposite sides cross the middle line and terminate 
in the interior of the olivary nuclei ; and the fibres of the superior peduncles, likewise 
decussating in the mesial plane before quitting the cerebellum, terminate in a grey 
centre in the interior of the tegmentum of the crus cerebri, named by Luys the 
superior olivary body. He further alleges that different fibres pass in all directions 
from the superior and inferior olivary bodies, and that thus the fibres of the cerebellum 
form a separate system indirectly connected Avith the fibres of the rest of the cerebro- 
spinal axis. Only a short notice, however, of these views having as yet been published, 
it will be necessary that the observations on which they are founded be made known 
and fully corroborated, before statements of so startling a nature can be generally 
accepted. (Luys, in Journ. de 1'Anat. et de Physiol., 1864, p. 225.) 



528 



THE CEREBELLUM. 



Microscopic Structure. The cortical grey matter which covers the foliated surface 
of the cerebellum is made up of the following elements, viz. : 1. Pellucid cells of 
considerable size. 2. Cells, for the most part of large size, and caudate, having the 
usual granular contents. These cells are embedded in a finely granular matrix ; the 
greater number of those of the caudate kind have a pyriform shape, and are prolonged 



Fig. 360. Fig. 360. THE COLUMNS OP THE 

MEDULLA OBLONGATA TRACED 
UPWARDS INTO THE CEREBELLUM 
AND CEREBRUM (from Arnold). | 

a, part of the anterior column 
which ascends in the olivary column ; 
6, decussating portion of the lateral 
column forming the pyramid and 
turned down ; c, olivary fasciculus 
ascending deeply through the pons ; 
d, olivary body ; e, restiform body; 
/, g, corpora quadrigemina ; c, h, i, 
the fillet ; h, the part which asoends 
to the cerebral peduncle ; i, the 
part passing up to the corpora 
quadrigemina ; m, m,', the trans- 
verse fibres of the pons divided ; n, 
inferior peduncle of the cerebellum ; 

o, septal fibres of the medulla oblongata ; q, fibres of the inferior peduncle continued 
into the laminse of the cerebellum ; ?, r, superior peduncle ; t, fasciculus teres ; u t 
thalamus ; v, corpus albicans. 




Fig. 361. Fig. 361. MINUTE STRUC- 

TURE OP THE SUBSTANCE 
OP THE CEREBELLUM (from 
Kolliker). 

A, large cells from the 
grey cortical substance of the 
human cerebellum. ~ 

a, three large cells exhibit- 
ing granular contents and a 
nucleus ; 6, the internal pro- 
cesses seen in two of the 
cells ; c, d, two external pro- 
cesses running towards the 
surface from two of the cells, 
in the third cell one large 
process only is seen; c', d', 
ramified finer parts of these 
processes. 

B, course of the nerve- 
tubes at the surface of the 
cerebellum, magnified with a 
low power. 

a, nerve of the medullary 
substance ; 6, nervus plexus 
of the substantia ferruginea ; 

c, border of that substance ; 

d, fine fibres running out 
from the dark -bordered tubes 
into the superficial grey sub- 
stance. 

at their small end into a simple or branched appendage, and this process, as first 
remarked by Purkinje, is in most of them directed towards the surface of the 
cerebellum. 3. Small bodies, like cell-nuclei densely aggregated without any inter- 
vening substance. These lie at some depth from the surface; according to Todd, 




MINUTE STRUCTURE OF CEREBELLUM. THE CEREBRUM. 529 

they form a thin light-coloured lamina, intermediate between two darker strata of 
grey matter which contain the nerve-cells ; one of these grey strata being the deepest 
and next the white matter of the cerebellum, while the other, which is the darker 
coloured of the two, is in contact with the pia mater. 4. Fibres. Tubular nerve- 
fibres pass from the white into the grey matter, and extend through it nearly as far 
as the surface. The mode of their termination, which is difficult to trace, has been 
investigated by various anatomists. According to Valentin, they form loops and 
return upon their course, but this statement has not been confirmed by other 
observers. 

Gerlach has recently described a very remarkable arrangement of the fibres of the 
cerebellum. According to him, these fibres, on approaching the grey matter, split 
up into extremely fine divisions, which form a network, while the granules, which he 
considers as small cells with ramifying processes, are placed at the angles of the 
meshes, and branching processes of the large nerve-cells also terminate in the network. 
According to Kb'lliker, networks of tubular fibres exist within the grey matter and 
communicate with the nerve-cells, while the granules belong to the reticulum of 
connective tissue. Luys, like Gerlach, describes lateral processes as being given oft' 
by the nerve-fibres to connect them with the granules, at the same time that they 
terminate likewise directly, although much attenuated, in the large nerve-cells. 
(Gerlach, "Microscopische Studien," pi. I., fig. 3; copied in Yirchow's "Cellular 
Pathology/' by Chance, p. 269.) 



THE CEREBRUM. 

The cerebrum, or brain proper, constitutes the highest and much the 
largest portion of the encephalon. It consists of the following parts, viz., 
the peduncular masses of the crura cerebri and processus a cerebello ad 
cerebrum ; the series of eminences or cerebral centres or ganglia concealed 
from view, named corpora quadrigemiua, optic thalami and corpora striata ; 
the cerebral hemispheres, which are by far the most bulky part of the cere- 
brum and of the whole encephalon, and form nearly the whole superficial 
part ; various commissural structures including the corpus callosum and 
fornix; and lastly some smaller structures, viz., the pineal and the pituitary 
bodies, and the olfactory bulbs. 

EXTERIOR OF THE CEREBRUM. 

The cerebral hemispheres together form an ovoid mass, flattened on its 
under side, and placed in the cranium with its smaller end forwards, its 
greatest width being opposite to the parietal eminences. They are separated 
in the greater part of their extent by the great longitudinal fissure. 

Each cerebral hemisphere has an outer or convex surface, which is in 
contact with the vault of the cranium ; an inner or flat surface, of a crescent 
shape, which forms one side of the longitudinal fissure ; and an irregular 
under surface, which rests on the base of the skull, and on the tentorium 
cerebelli. 

Three lobes, or large divisions, projecting in three different directions, have 
usually been distinguished in each hemisphere, under the names of anterior, 
middle, and posterior lobes. The division between the anterior and middle 
lobes is very clearly denned below and on the sides by a deep cleft, named 
the Sylvian fissure. There is no similar demarcation between the middle 
and posterior lobes ; but anatomists have generally considered as the pos- 
terior lobe that part of the hemisphere which lies over the cerebellum. 
The under surface of the anterior lobe is triangular and excavated to adapt 
it to the roof of the orbit on which it rests. The middle lobe is rounded 



530 



THE CEREBRUM. 



and prominent, and occupies the middle fossa of the skull the edge of the 
lesser wing of the sphenoid bone corresponding with the Sylvian fissure. 

Fig. 362. UPPER SUR- 
FACE OF THE BRAIN 

SHOWING THE CONVO- 
LUTIONS (from R. Wag- 
ner). 4 

This view was taken 
from the brain of a 
famous mathematician, 
Professor C. F. Gauss, 
who died in 1854, aged 
78. It is selected as 
an example of a well- 
formed brain of the 
usual size with fully 
developed convolutions. 
a, superior or first 
frontal convolution ; a', 
second or middle frontal ; 
", third or inferior 
frontal ; A, A, anterior 
ascending parietal con- 
volution ; B, B, pos- 
terior ascending parietal 
convolution ; b, first or 
upper parietal convolu- 
tion ; b', second or mid- 
dle ; b", third or in- 
ferior ; c, first or upper 
tempoi'al convolution ; 
d, first or upper occipi- 
tal convolution ; d', 
second or middle ; d", 
third or lower ; I, I, the 
superior longitudinal fis- 
sure ; r, the fissure of Rolando ; p, the external perpendicular fissure. 

The posterior lobe is smooth and slightly concave on its under surface, 
where it rests on the arch of the tentorium. 

It is right to remark that some anatomical writers have admitted only two lobes, 
reckoning the middle and posterior lobes as one, under the name of the posterior 
lobe ; while others more recently have divided the middle lobe into two, an upper 
and lower, and have added that of the island of Reil, so as to make five principal 
lobes in all. These have been named respectively the frontal, parietal, temporal, 
occipital, and central lobes. 

The great longitudinal fissure, seen upon the upper surface of the brain, 
extends from before backwards throughout its whole length in the median 
plane, and thus separates the cerebrum, as already stated, into a right and 
left hemisphere. On opening this fissure, it is seen, both before and behind, 
to pass quite through to the base of the cerebrum : but in the middle it is 
interrupted by a large transverse mass of white substance, named the 
corpus callosum, which connects the two hemispheres together. While the 
brain is in its natural situation, this fissure is occupied by a vertical process 
of the dura mater the falx cerebri which dips down between the two 
hemispheres, not quite reaching to the corpus callosum. 

The Sylvian fissure, which separates the anterior and middle lobes, passes 
at first upwards and backwards in the outer part of the hemisphere, and 




FORM AND DIVISIONS OF THE CEREBRUM. 531 

divides into two branches, anterior and posterior. It lodges the trunk and 
primary divisions of the middle cerebral artery, and at its commencement 
presents a spot pierced by numerous small arterial branches, and thence 
named the locus perforatus anticus. 

The surface of the hemispheres is composed of grey matter, and is moulded 
into numerous smooth and tortuous eminences, named convolutions, or gyri, 
which are marked off from each other by deep furrows, called sulci, or 
anfractuosities. 

Fig. 3G3. 




Fig. 363. LATERAL VIEW OF THE RIGHT CEREBRAL HEMISPHERE (from Sappey 
after Foville). 

1, fissure of Rolando ; 2, anterior ascending parietal convolution ; 3, frontal convolu- 
tions connected posteriorly with the anterior ascending parietal ; 4, union of two frontal 
convolutions ; 5, posterior ascending parietal convolution ; 6, another parietal convolution 
similarly Connected with those on the inner surface ; 7, 7, anterior part of the convolu- 
tion of the fissure of Sylvius; 8, 8, horizontal part of the same convolution; 9, 9, 
posterior part ; 10, 11, 12, anterior, middle, and posterior principal convolutions of the 
island of Reil or central lobe ; 13, supraorbital convolution ; 14, part of the temporal 
lobe ; 15, occipital lobe. 

CEREBRAL CONVOLUTIONS. The convolutions are covered closely through- 
out by the vascular investing membrane, the pia mater, which sends pro- 
cesses down to the bottom of the sulci between them, while the serous 
covering, the arachnoid membrane, passes from one convolution to another, 
over their summits and without dipping between them. The sulci are 
generally from half an inch to an inch in depth ; but in this respect there 
is much variety in different brains, and in different parts of the same brain ; 
those upon the outer convex surface of the hemisphere being the deepest. 
In general, the depth of a convolution exceeds its thickness ; and its thick- 
ness, near the summit, is somewhat greater than through its base. 

Since the external grey or cortical substance is continuous over the whole 
surface of the cerebral hemispheres, being found alike within the sulci and 
upon the gyri, a far greater extent of grey matter is thus exposed to the 
vascular surface of the pia mater with a given size of the brain, than could 
have been the case had the hemispheres been plain and destitute of 
convolutions. 

The general arrangement of the convolutions has been made the subject 



532 THE CEREBRUM. 

of study by various anatomists in earlier and recent times, but still re- 
quires farther elucidation. An attempt to describe minutely all the indi- 
vidual gyri would be difficult and useless, owing to their irregularity in 
different cases, and their want of symmetry in the same brain. .Nevertheless, 
there are some sufficiently constant in presence, and characteristic in situa- 
tion and form, to admit of being specially described ; and it seems probable 
that, by a sufficiently careful comparison of the convolutions in different 
animals, and the observation of their development in the foetus, certain 
general facts may be ascertained regarding them, tending to throw light 
upon their disposition in man. 

Fig. 364. 




Fig. 364. OUTLINE OP THE CHREBRUM AS SEEN FROM THE LEFT SIDE, SHOWING THE 
CONVOLUTIONS AS DISTINGUISHED BI GRATIOLET. f 

F, frontal lobe ; P, parietal lobe ; T, temporal lobe ; 0, occipital lobe ; R, R, fissure 
of Rolando ; s, s. fissure of Sylvius, posterior division : s', s', its anterior division ; C, at 
the junction of the two, marks the place of the central lobe or convolutions of the island 
of Reil ; p, the place of the vertical or occipital fissure ; , a', a", superior, middle and 
inferior frontal convolutions ; a*, supraorbital convolutions ; A, anterior transverse or 
ascending parietal convolution ; B, posterior transverse or ascending parietal convolution ; 
&, &', b", upper, middle and lower parietal convolutions ; c, c', c", upper, middle and 
lower temporal convolutions; d, d', d", upper, middle and lower occipital convolutions ; 
between b, b', b", and d, d' } d", are seen the connecting convolutions ; between c and c', 
the parallel fissure. 

The island of Reil constitutes the set of convolutions (gyri operti) which 
appear earliest both in the fostus and in the animal series, It is a 
triangular eminence, broken externally into short radiating convolutions, 
which forms a delta between the anterior and posterior division of the 
fissure of Sylvius, and is limited externally by a deep sulcus. This mass, 
constituting the central lobe of recent authors, derives additional interest 
from being the centre round which the principal convolutions of the cere- 
brum are arranged. It is only brought into view by laying open the fissure 
of Sylvius. (See Figs. 368 and 377.) 

The convolution of the Sylvian fissure is a very large convolution, which is 
also early in its appearance in animals. Commencing in front of the inner 
end of the Sylvian fissure, it takes a tortuous and much folded course all 
round that fissure, giving off numerous secondary gyri, and terminates behind 
the fissure opposite the point where it began. 

The gyrus fornicatus, convolution of the corpus callosum, or internal con- 



CEREBRAL CONVOLUTIONS. 633 

volution, is one of the most distinct and symmetrical convolutions in the 
whole brain. Commencing on the under surface of the brain, immediately 
before the anterior perforated space, it ascends a short distance in front of 
the anterior recurved extremity of the corpus callosum, and then runs back- 
wards immediately above that body, as far as its posterior extremity : there 
it turns downwards and forwards, embracing the cerebral peduncle, to reach 
the entrance of the Sylvian fissure. This long convolution, therefore, describes 
a sort of arch or ring, open or interrupted opposite the Sylvian fissure, and 
embracing the corpus callosum above, and the cerebral peduncle below. It 
thus, as was pointed out by Foville, forms a sort of rim or border to the 
grey matter ; whence it is named by him convolution d'ourlet. The surface 
of this convolution, especially towards its inferior termination, is covered by 
a very thin cribriform layer of white substance, which, with the grey matter 
beneath, gives the surface a mottled aspect. This has been called the reti- 
culated white substance. 

The marginal convolution of the longitudinal fissure is a large convolution 
which may be traced, more or less indented or interrupted however in its 
course, along the line of junction between the convex and flat surfaces of 
the hemisphere, forming the lip of the great longitudinal fissure. Ifc com- 
mences on the under surface of the brain, in common with the gyrus 
fornicatus, and, passing forwards, forms the inner border of the triangular 
orbital surface of the anterior lobe. In this part it is cleft longitudinally 
by a deep sulcus, into which the olfactory bulb is received, and which, it may 
be mentioned, is developed at an earlier period than the convolution itself. 
On the front and upper surface of the cerebrum, this convolution may 
generally be traced for some distance along the margin of the longitudinal 
fissure, but soon becomes marked by deep sulci ; and, thus interrupted, may 
be followed round the posterior extremity, and along the under surface of 
the hemisphere forwards as far as the point of the middle lobe, running 
parallel for some space with the under portion of the gyrus fornicatus. Two 
of the sulci which interrupt the marginal convolution are very constant, 
viz., the vertical fissure with the fissure of the hippocampi, and the fissure 
of Rolando. 

The fissure of the hippocampi has a deep origin in the inner margin of the 
middle lobe of the brain between the fascia dentata and the gyrus fornicatus, 
and, passing backwards, crosses that gyrus on the under surface of the brain, 
behind the corpus callosum, and proceeds in a nearly horizontal course along 
the inner face of the hemisphere. This fissure is important as forming the 
reverse of the elevations of the hippocampi in the interior of the brain, and 
as being (according to Reichert) produced at an early period in connection 
with the general development of the hemispheres, and being comparable 
therefore rather to the fissure of Sylvius than to a mere sulcus. The part 
of the gyrus fornicatus beneath this fissure is distinguished as the gyrus 
hippocampi. 

The fissure of Rolando, starting from behind the vertex, runs outwards and 
forwards from the longitudinal fissure, so that the right and left grooves 
form a V-shaped line open in front. It derives its importance from being 
characteristic of the form of the brain of man and the quadrumana, and 
separating two considerable convolutions, which extend from the superior 
longitudinal fissure to the fissure of Sylvius. These convolutions, peculiar 
to the greater number of simise and attaining their fullest development in 
man, constitute the anterior and posterior transverse or anterior and 
posterior ascending parietal convolutions. 



634 THE CEREBRUM. 

The vertical fissure of recent authors crosses the marginal convolution in the 
posterior part of the cerebrum, extending slightly outwards upon its upper surface 
and more deeply on its internal aspect, so as to form a separation between the 
so-called parietal and occipital lobes. 

According to Foville the convolutions may be arranged in four principal orders, 
founded in a great measure on their relative connections with the anterior perforated 
space, which, in his estimation, is a part of the highest importance. 

The first order issues from the perforated space, and consists of two portions. One, 
large and vertical, is the gyrus fornicatus, without its ascending secondary gyri ; the 
other, short and horizontal, is the slightly elevated ridge which bounds the perforated 
space in front and on the outer side. 




Fig. 365. RIGHT HALF OE THE BRAIN DIVIDED BY A VERTICAL ANTERO -POSTERIOR 
SECTION (from various sources and from nature), i 

1, great superior or marginal convolution ; 2, convolution of the corpus callosum ; 3, 
secondary convolutions running between this and the preceding ; within the numbers 
2, 2, 2, the corpus callosum ; 4, the fifth ventricle ; 5, the third ventricle (see Fig. 377 
for a larger view of these parts) ; 5', pituitary body; 6, immediately behind the corpora 
quadrigemina and pineal gland; +, the fourth ventricle; 7, pons Varolii ; 8, medulla 
oblongata ; 9, cerebellum ; the middle lobe showing the section of the arbor vitse ; I, the 
olfactory bulb ; II, the right optic nerve ; the commissure cut through ; III, the right 
nerve of the third pair. 

The second order, also consisting of two portions, commences from the horizontal 
portion of the first order on the limits of the perforated space. One part corresponds 
with the marginal convolution of the longitudinal fissure, as already described, except 
that part of it on the orbital surface of the anterior lobe which lies to the outer side 
of the olfactory sulcus ; the other part is the convolution of the Sylvian fissure. 

The third order consists of two sets, of which one occupies the inner surface of the 
hemisphere, and connects the gyrus fornicatus in its whole length with the marginal 
convolution of the longitudinal fissure ; the other set lies in the Sylvian fissure, forms 
the island of Reil, and connects the short horizontal portion of the first order with 
the convolution surrounding that fissure. 

The convolutions of the fourth order, the largest, deepest, and least symmetrical of 
all, are quite detached from the perforated space, and have no relation to the first 
order of convolutions. They connect the two convolutions of the second order 



CEREKRAL CONVOLUTIONS. 



635 



together, viz., the marginal convolution of the median fissure and that of the Sylvian 
fissure, and occupy the outer or convex surface of the cerebral hemisphere. 

Leuret, by an extended comparison of the brains of different animals, was led to 
divide mammals into fourteen groups, according to the disposition of the convolutions. 

In the lowest or simplest group, including the bat, mole, and rat, the Sylvian 
fissure is the only division of the surface present, or along with it a few very slight 
sulci. In a higher group, containing the fox and dog, and presenting in a marked 
form the t} r pical mode of division, Leuret recognises as fundamental six convolutions 
four external, including the superior marginal and that of the fissure of Sylvius, 
and two internal, viz., the supraorbital and gyrus fornicatus. In other groups, 
together with various other modifications of form by subdivision or by union through 
supplemental ones, the number of the fundamental convolutions is frequently reduced 
to five or to four. 

In the brain of the elephant, on the other hand, placed by Leuret in the thirteenth 
group, he recognises the superior transverse convolutions; and in the last group, 
comprehending the quadrumana, these transverse convolutions are two in number, 
and are separated by the groove, named by Leuret fissure of Rolando. These trans- 
verse or ascending parietal convolutions are a constant and well-marked feature of the 
human bi'ain, in which they attain their highest development. 

Fi-. 366. 




Fig. 366. OUTLINE OP THE INNER SURFACE OP THE EIGHT HALF OP THE BRAIN, 

SHOWING THE PRINCIPAL LOBES AND CONVOLUTIONS ACCORDING TO GrRATIOLET. 

F, frontal lobe ; P, parietal ; 0, occipital ; T, temporal ; r, fissure of Rolando ; /, 
fronto-parietal fissure ; p', inner perpendicular or occipito -parietal fissure ; h, the calca- 
rine fissure of Huxley, and with the line continued forwards between g and h', the hippo- 
campal fissure ; ti, convolution of the hippocampus ; g, gyrus fornicatus or convolution 
of the corpus callosum ; s, Sylvian fissure ; I, olfactory bulb ; II, optic nerve ; III, third 
nerve; C, cerebellum. 



More recently, Gratiolet has arranged the convolutions with great detail, according 
to their most distinguishing common features in man and the simiae. On the 
external surface of the hemisphere he distinguishes five lobes, viz., the frontal and 
parietal above the fissure of Sylvius ; the temporo-splienoidal below that fissure ; the 
occipital behind it, and the island of Reil, or central lobe, within the fissure. The 
frontal lobe he divides into an orbital and a frontal portion, and in the frontal portion 



536 THE CEREBRUM. 

he distinguishes a superior, middle, and inferior tier of convolutions. In the parietal 
lobe are the anterior and posterior ascending convolutions (convolution of Rolando) 
surrounding the fissure of Rolando, and behind these a curved lobe. In the temporo- 
sphenoidal lobe are described a superior, middle, and inferior convolutions, lying 
parallel to the fissure of Sylvius. The occipital lobe presents also three tiers, but less 
distinct than those of the frontal, and besides these are four convolutions uniting the 
occipital and parietal lobes, named by Gratiolet plis de passage, or the connecting 
convolutions. 

The internal surface^ of the hemisphere Gratiolet divides into the fronto-parietal 
lobe, corresponding in extent to the frontal and parietal lobes of the external surface, 
and limited behind by the internal perpendicular fissure, the occipital lobe between 
that fissure and the fissure of the hippocampi; and the occipito-temporal lobe, 
including the tentorial surface, and extending outwards to the sphenoido-temporal 
lobe. 

It is to be remarked, however, that the divisions and nomenclature of Gratiolet, 
however useful they may be for the purpose of explicit comparison of the convolu- 
tions of the human brain with those of the quadrumana, the study in which the 
inventor has made use of them, are yet of a somewhat artificial description, and may 
not be applicable to a more extended comparison of the disposition of the convolu- 
tions among animals. 

From Reichert's plates it is apparent that the internal perpendicular fissure (occi- 
pito-parietal of Huxley) is the upper of two branches into which the fissure of the 
hippocampi divides posteriorly in its first development, and which together with 
that fissure constitutes his fissura occipitalis. The inferior branch, the posterior 
part of the fissure of the hippocampi, is the calcarine fissure of Huxley. 

Not only the comparison of the brain of man with those of other animals, but like- 
wise the comparison of human brains one with another, establishes the existence of a 
relation between mental development and the complication, size, and depth of the 
cerebral convolutions, and the extent of the grey matter contained in them. 

On the subject of the cerebral convolutions the reader may consult, in addition to 
the works of Arnold, Tiedemann, Foville and Reichert, that of Leuret and Gratiolet 
"Anat. Comp. du Systeme Nerveux, 1839-57;" Gratiolet, "Mem. sur les Plis 
C6re"braux de 1'Homme et des Primates, 1854 ; " R. Wagner, " Tiber die typischen 
Verschiedenh. der Windungen der Hemispharen," &c., Getting. 1860-62 ; Huschke, 
" Schadel, Hirn und Seele," 1854 ; Huxley, " Brain of Ateles paniscus," Proc. of 
Zool. Soc., June, 1861 ; J. Marshall, (( On the Brain of a Bush-woman, and on the 
Brains of Two Idiots, &c.," Trans. Roy. Soc. 1863. 

BASE or THE CEREBRUM. When the brain is turned with its base upper- 
most, and the parts of which it is composed are allowed to fall slightly 
asunder by their own weight, two considerable masses, consisting of white 
substance externally, are seen emerging together from the fore part of the 
poiis Yarolii, and, separating from each other as they proceed forwards and 
outwards, to enter the inner and under part of the right and left cerebral 
hemispheres. These white masses, which are marked on the surface with 
longitudinal striae, and have somewhat the appearance of large bundles of 
fibres, are the peduncles or crura of the cerebrum. Immediately before 
entering the corresponding hemisphere, each is crossed by a flattened white 
cord, named the optic tract, which, adhering by its upper border to the 
peduncle, is directed forwards and inwards, and meets in front with its 
fellow of the opposite side to form the optic commissure, from the fore part 
of which the optic nerves proceed. 

Limited behind by these diverging peduncles, and in front by the con- 
verging optic tracts, is a lozenge-shaped interval, called the interpeduncular 
space, in which are found, in series from behind forwards, the posterior per- 
forated space, the corpora albicantia, and the tuber cinereum, from which 
is prolonged the infundibulum attached to the pituitary body. 

The posterior perforated space (locus perforatus posterior) is a deep fossa 



PARTS IX THE IXTERPEDUXCULAR SPACE. 537 

situated between the peduncles, the bottom of which is composed of greyish 
matter, connecting the diverging crura together, and named pons Tarini. 
It is perforated by numerous small openings for the passage of blood-vessels ; 
and some horizontal white striae usually pass out of the grey matter and turn 
round the peduncles immediately above the pons. 

Fig. 367. 




Fig. 367. BASE OP THE BRAIN WITH THE ORIGINS OP THE CEREBRAL NERVES. ^ 

This figure is taken from an adult male brain which had been hardened in alcohol. 

1, superior longitudinal fissure ; 2, fissure of the olfactory tract and lower part of the 
superior convolution ; 2', orbital convolutions; 2", external or inferior frontal convolu- 
tion ; 3, inner part of the fissure of Sylvius, near the anterior perforated spot ; 3, 3, outer 
part; 4, inner convolution of the temporal lobe; 4', middle convolution; 4", outer con- 
volution; 5, 5', occipital lobe; 6, on the right pyramidal body of the medulla oblongata 
above the decussation ; 7, amygdaloid lobe of the cerebellum ; 8, biventral lobe ; 9, 
lobulus gracilis ; 10, posterior inferior lobe ; +, the inferior vermiform process; I, 
olfactory bulb ; I', the tract divided on the left side, showing the three white striai by 
which it is connected with the brain ; II, in the anterior perforated spot, marks the right 
optic nerve; the left has been cut short; III, on. the right crus cerebri, denotes the third 
pair ; IV, on the inner convolution of the middle lobe, the fourth pair ; V, the trige- 
minus; VI, on the pons Varolii, the sixth ; VII, also on the pons Varolii, the seventh ; 
VIII, on the left lobe of the cerebellum below the horizontal fissure and the flocculus, 
denotes the eighth pair; IX, on the upper part of the right amygdaloid lobe, denotes 
the ninth pair ; X, on the same, the suboccipital nerve. 

The corpora albicantia or mammillaria are two round white eminences in 
front of this fossa, each about the size of a small pea, surrounded by grey 
matter, and connected together across the middle line. 

The corpora albicantia are formed, as will hereafter be explained, by the anterior 
extremities of the fornix ; hence they have also been named bulbs of thefornix. In 



538 



THE CEREBRUM. 



the foetus they are at first blended together, and they become separated about the 
beginning of the seventh month. In most vertebrate animals there is but one white 
eminence or corpus albicans in their place. 

Fig. S68. Fig. 368. VIEW FROM 

BEFORE OF THE ME- 
DULLA OBLONGATA, 
PONS VAROLII, CRURA 
CEREBRI, AND OTHER 
CFNTRAL PORTIONS OF 
THE ENCEPHALON. 

On the right side the 
convolutions of the cen- 
tral lobe or island of Eeil 
have been left, together 
with a small part of the 
anterior cerebral convolu- 
tions : on the left side 
these have been removed 
by an incision carried 
betweon the thalamus 
opticus and the cerebral 
hemisphere. 

I', the olfactory tract 
cut short and lying in its 
groove between two con- 
volutions ; II, the left 
optic nerve in front of 
the commissure^; II', the 
right optic tract ; Th, 
the cut surface of the left 
thalamus opticus ; C, the 
central lobe or island of 
Reil ; Sy, fissure of 
Sylvius ; x x , locus 
pevforatus anterior ; e, 
the external, and i, the 
internal corpus genicu- 
latum ; h, the hypophysis 
cerebri or pituitary body ; 
tc, tuber cinereum with 
the infundibulum ; a, one 
of the corpora albicantia ; 
P, the cerebral peduncle 
or crus ; /, the fillet ; 
III, close to the left 
oculo-motor neive ; x, 
the locus perforates pos- 
ticus; PV, pons Varolii ; 

V, the greater root of the fifth nerve ; +, the lesser or motor root ; on the right side 
this + is placed on the Gasserian ganglion, arid points to the lesser root, where it proceeds 
to join the inferior maxillary nerve ; 1, ophthalmic division of the fifth nerve ; 2, superior 
maxillary division ; 3, inferior maxillary division ; VI, the sixth nerve ; VII a, the 
facial ; VII b, the auditory nerve; VIII, the pneumo-gastric nerve ; Villa, the glosso- 
pharyngeal ; VIII b, the spinal accessory nerve ; IX, the hypoglossal nerve ; fl, the floc- 
culus ; fh, the horizontal fissure of the cerebellum (Ce) ; am, the amygdala; pa, the 
anterior pyramid ; 0, the olivary body ; r, the restiform body ; d, the anterior median 
fissure of the spinal cord, above which the decussation of the pyramids is represented ; 
ca, the anterior column ; cl, the lateral column of the spinal cord ; C I, the suboccipital 
or first cervical nerve. 

The tuber cinereum is a lamina of grey matter extending forwards from 
the corpora albicantia to the optic commissure, to which it is attached, and 
forming, as afterwards described, part of the floor of the third ventricle. 




ca 



PARTS SEEX IX THE BASE OF THE CEREBRUM. 539 

In the middle it is prolonged into a hollow conical process, the infundi- 
bulum, to the extremity of which is fixed the pituitary body. 

The pituitary body or hypophysis cerebri, formerly called pituitary gland, 
from its being erroneously supposed to discharge pituita ii,to the nostrils, is 
a small reddish grey mass, of a somewhat flattened oval shape, widest in the 
transverse direction, and occupying the sella turcica of the sphenoid bone. 
It consists of two lobes, of which the anterior is larger, and concave behind, 
where it embraces the smaller posterior lobe. Its weight is from five to ten 
grains. In the adult it is solid, and of a firm consistence. 

The anterior lobe consists of two kinds of matter, one hard and grey, the 
other, situated within, softer and of a yellowish white colour. The posterior 
lobe is darker and redder than the anterior. Both are very vascular. 

The pituitary body appears to approach in structure to the vascular or duct" 
less glands, such as the thyroid and suprarenal bodies, &c. According to Sharpey's 
observations, with which those of subsequent writers agree, it differs greatly in 
structure, at least in its anterior and larger lobe, from any other part of the ence- 
phalon. The substance of the anterior lobe appears to be constituted by a mem- 
branous tissue forming little round cavities or loculi, which are packed full of 
nucleated cells. The loculi are formed of transparent, simple membrane, with a few 
fibres and corpuscles resembling elongated cell-nuclei disposed round their walls. 
The cells contained in the cavities are of various sizes and shapes, and not unlike 
nerve-cells or ganglion-globules ; they are collected into round clusters, filling the 
cavities, and are mixed with a semi-fluid granular substance. This thin granular 
matter, together with the cells and little specks of a clear glairy substance like 
mucus, can be squeezed from the cut surface, in the form of a thick, white, cream-like 
fluid. 

In the foetus, the pituitary body is proportionally large, and contains a cavity 
which communicates, through that of the infundibulum, with the third ventricle. 
This body is constantly present, and has the same connection with the brain in all 
vertebrate animals. 

In the middle line of the base of the brain, in front of the optic commis- 
sure, is the anterior portion of the great longitudinal fissure, which passes 
down between the hemispheres. At a short distance in front of the com- 
missure, this fissure is crossed transversely by a white mass, which is the 
anterior recurved extremity of the corpus callosum. On gently turning back 
the optic commissure, a thin connecting layer of grey substance, the lamina 
cinerea, is seen occupying the space between the corpus callosum and the 
commissure, and continuous above the commissure with the tuber cinereum. 
It is connected at the sides with the grey substance of the anterior perforated 
space, and forms part of the anterior boundary of the third ventricle : it is 
somewhat liable to be torn in removing the brain from the skull ; and, in 
that case, an aperture would be made into the fore part of the third 
ventricle. 

At a short distance outwards from the lamina cinerea is the anterior per- 
forated spot (locus perforatus anticus), a depression near the entrance of the 
Sylvian fissure, floored with grey matter, and pierced with a multitude of 
small holes for the passage of blood-vessels, most of which are destined for 
the corpus striatum, the deeper portion of the brain beneath which it lies. 

The grey surface of each perforated space is crossed by a broad white 
band, which may be traced from the middle of the under surface of the 
corpus callosum in front, backwards and outwards along the side of the 
lamina cinerea towards the entrance of the Sylvian fissure. These bands of 
the two sides are named the peduncles of the corpus callosum. 

When the entire encephalon is viewed from below, the back part of the 



540 



THE CEKEBRUM. 



tinder surface of the cerebrum is concealed by the cerebellum and the pons 
Varolii. If, however, these parts be removed, it will be seen that the tw o 
hemispheres of the cerebrum are separated behind as they are in front, by 
the descent of the great longitudinal fissure between them, and that this 
fissure is arrested by a cross mass of white substance, forming the posterior 
extremity of the corpus callosum. This posterior part of the great longi- 
tudinal fissure is longer than the anterior portion. 



INTERNAL PARTS OF THE CEREBRUM. 



The anatomy of the interior of the cerebrum is most conveniently studied 
by removing, after the manner of Vieussens and Vicq-d'Azyr, successive 
portions of the hemispheres by horizontal sections, beginning from above. 



Fig. 



Ik 




Fig. 369. VIEW OP THE CORPUS CALLOSUM FROM ABOVE (from Sappey after Foville). ^ 

The upper surface of the corpus callosum has been fully exposed by separating the 
cerebral hemispheres and throwing them to the side; the gyrus fornicatus has "been 
detached, and the transverse fibres of the corpus callosum traced for some distance into 
the cerebral medullary substance. 

1, the upper surface of the corpus callosum ; 2, median furrow or raphe ; 3, longi- 
tudinal strise bounding the furrow ; 4, swelling formed by the transverse bands as they 
pass into the cerebrum ; 5, anterior extremity or knee of the corpus callosum ; 6, pos- 
terior extremity ; 7, anterior, and 8, posterior part of the mass of fibres proceeding from 
the corpus callosum ; 9, margin of the swelling ; 10, anterior part of the convolution of 
the corpus callosum; 11, hem or band of union of this convolution; 12, internal con- 
volutions of the parietal lobe; 13, upper surface of the cerebellum. 

The first horizontal section, to be made about half an inch above the 
corpus callosum, displays the internal white matter of each hemisphere, 
speckled with red spots where its blood-vessels have been divided, and sur- 



THE CORP (IS CALLOSUM. 541 

rounded on all sides by the grey matter which is seen to follow closely 
the convoluted surface, and to be of nearly equal thickness at all points. 
This white central mass in each hemisphere was named by Vicq-d'Azyr 
centrum ovale minus. On separating the remaining portions of the two 
hemispheres from each other, two sulci are seen to exist between the corpus 
callosurn and the gyri immediately in contact with it, viz., the gyrus 
fornicatus of each side. These sulci were distinguished by the older anatomists 
as ventricles of the coitus callosum. 

Another section being made at the level of the corpus callosum, the 
white substance of that part is seen to be continuous with the internal 
medullary matter of both hemispheres : and the large white medullary mass 
thus displayed, surrounded by the border of cortical substance, constitutes 
what is generally described as the centrum ovale, of Vieussens. 

The corpus callosum or great commissure (trabs cerebri) is a white struc- 
ture, with a length not quite half of that of the brain, and approaching 
about two-fifths nearer to the front than the back of the hemispheres. It 

Fig. 370. 




Fig. 370. HORIZONTAL SECTION OP THE BRAIN SHOWING THE LATERAL VENTRICLES AND 
THE FIFTH VENTRICLE OPENED (from Sappey after Vicq-d'Azyr). ^ 

1, the fifth, ventricle ; 2, the two laminse of the septum lucidum meeting in front of 
it ; 3, lesser hippocampus of the posterior cornu ; 4, horizontal section of the posterior 
swelling of the corpus callosum; 5, middle part of the fornix, where it has been separated 
from the corpus callosum ; 6, posterior pillar of the fornix ; 7, hippocampus major 
descending in the middle cornu ; 8, eminentia collateralis ; 9, lateral parts of the fornix ; 
10, choroid plexus ; 11, tsenia semicircularis ; 12, corpus striatum. 

is about an inch in width behind, and somewhat narrower in front. Its 
thickness is greater at the ends than in the middle, and is greatest behind, 



542 



THE CEREBRUM. 



where it is nearly half an inch. It is arched from before backwards. Its 
upper surface is distinctly marked by transverse furrows, which indicate 
the direction of the greater number of its fibres. It is also marked in the 
middle by a slight longitudinal groove, the raphe, which is bounded laterally 
by two white tracts, placed close to each other, named striae longitudinales, 
or nerves of Lancisi. On each side, near the margin, are seen other 
longitudinal lines (striae longituclinales laterales) occasioned by a few scanty 
white fibres. 

In front, the corpus callosum is reflected downwards and backwards, 
between the anterior lobes, forming a bend named the genu. The inferior 
or reflected portion, which is named the rostrum, becomes gradually nar- 
rower as it descends, and is connected by means of the lamina cinerea with 
the optic commissure. It also gives off the two bands of white substance, 
already noticed as the peduncles of the corpus callosum, which, diverging 
from one another, run backwards across the anterior perforated space on 
each side to the entrance of the Sylvian fissure. 



Fig. 371. 




semicircularis ; y, enrinentia collaterals. 



Fig. 371. THE LATERAL 
VENTRICLES OPENED BY 
A HORIZONTAL SECTION, 
AND THE MIDDLE CORNU 
EXPOSED ON THE RIGHT 

SIDE. 

a, b, anterior and pos- 
terior parts of the great 
longitudinal fissure ; c, 
section of the anterior part 
of the corpus callosum ; d, 
posterior part of the same ; 
e, the left choroid plexus ; 
/, the fornix ; g, the an- 
terior; 7t, the posterior, 
and q, the descending 
cornu of the lateral ven- 
tricle ; k, Jc, corpora 
striata ; I, I, optic tha- 
larai ; n, n, right and left 
hippocampus minor ; o, 
posterior pillar of the for- 
nix ; v, the corpus fimbri- 
atura into which it passes; 
<?, cornu ammonis or pes 
hippocampi ; A, the medul- 
lary substance of the cere- 
bral hemisphere ; r, part 
of the cortical substance 
showing alternate grey and 
white matter ; s, s, tsenia 



Behind, the corpus callosum terminates in a free thickened border (bour- 
relet, pad), the under surface of which is also free for a short distance 
forwards. 

The under surface of the corpus callosum is connected behind with the 
fornix, a structure to be presently described, and in the rest of its length 
with the septum lucidum, a vertical partition between the two lateral ven- 
tricles. 



THE LATERAL VENTRICLES. 543 

Although it presents a few longitudinal white fibres on its surface, the corpus cal- 
losum consists almost entirely of fibres having a transverse course towards each side, 
and spreading in a radiating manner into the substance of the two hemispheres. As the 
transverse fibres from the anterior and posterior lobes of the cerebrum are necessarily 
aggregated in large numbers near the corresponding ends of the corpus callosum, its 
greater thickness at those points, in comparison with the rest of its extent, is 
accounted for ; and, since the posterior lobe reaches further beyond the corpus callosum 
than the anterior, the greater thickness behind is also explained. 

LATERAL VENTRICLES, or ventriculi tricornes. By dividing the fibres of 
the corpus callosum in a longitudinal direction at a short distance on each 
side of the middle line, and about midway between the two ends of the 
hemispheres, an opening is made into the right and left lateral ventricles of 
the brain. These ventricles form part of the general ventricular space 
within the cerebrum ; they are serous cavities, and are lined by a delicate 
epitheliated structure, the ependyma ventriculorum, which at certain parts in 
the adult, and probably throughout its whole extent in the foetus, is pro- 
vided with cilia. In the natural state, the walls of the ventricles are moist- 
ened internally with a serous fluid, which sometimes exists in considerable 
quantity, even in a healthy brain. 

It was formerly a subject of dispute whether the lining of the ventricles consisted 
of epithelium only, or also of a membrane. The progress of the histology of the 
brain has solved the problem in a manner which leaves the disputants on both sides 
partially in the right. It is now recognised that a peculiar form of connective tissue is 
found throughout the substance of the brain, similar to that which has been described 
in the spinal cord. A layer of this substance, unmixed with nerve-tissues, but in direct 
continuity with the interstitial web, and not a distinct membrane, supports the 
epithelium. It is of the same nature as the substance immediately surrounding the 
central canal of the spinal cord, and is named by Virchow neuroglia (Virchow's 
" Cellular Pathology," by Chance, p. 273). 

The form of the epithelial cells appears to vary in different parts ; these cells 
being, according to Kb'lliker, of the flat pavement kind in the third ventricle, and 
more spherical in the lateral ventricles ; and, according to Gerlach, cylindrical in the 
aqueductus Sylvii. 

From the central part or body of each lateral ventricle the cavity is 
extended into each of the three lobes of the hemisphere, thus forming 
an anterior, a posterior, and a middle or descending cornu. 

The body of each lateral ventricle is roofed in by the corpus callosum, and 
is separated from its fellow by a vertical partition, the septum lucidum, 
which descends from the corpus callosum to the fornix. In the floor of the 
ventricle there is seen most posteriorly one half of the fornix, which is a 
thin layer of white brain-substance, broad behind and narrow in front : 
external and anterior to this is the choroid plexus of the lateral ventricle, a 
red vascular fringe, forming the border of the velum interpositum, a fold 
of pia mater extending inwards, on which the fornix rests : external and 
anterior to the choroid plexus is the anterior and outer part of the optic 
thalamus, appearing from beneath it : outside and in front of the thalamus 
is the corpus striatum ; and between those two bodies is a narrow flat band, 
the tcpnia semicircularis. 

The anterior cornu is the blind anterior extremity of the ventricle, pro- 
jecting a little way into the anterior lobe. It is covered by the corpus 
callosum, and turns forwards and outwards round the anterior free extremity 
of the corpus striatum, descending as it proceeds, and bounded behind by 
that body, and in front by the reflected part of the corpus callosum. 

The middle or descending cornu turns round the back part of the optic 



544 



THE CEREBRUM. 



thalamus, which appears in its cavity and forms its anterior boundary, 
while its remaining boundaries are formed by the hemisphere. At its com- 
mencement it is directed backwards and outwards ; then, passing downwards 
with a sweep, it curves forwards, and at its extremity has a marked inclina- 
tion inwards. The principal object seen upon the floor of this cornu is the 
hippocampus major (pes hippocampi, or cornu ammonis), a large white 
eminence extending the whole length of the cornu. The hippocampus 
major becomes enlarged towards its anterior and lower extremity, and is 
indented or notched on its edge, so as to present some resemblance to the 
'paw of an animal, whence, no doubt, its name of pes hippocampi. The 
white fibres of its surface are directed obliquely backwards and outwards 
across it: they form only a thin smooth layer, and beneath them is cineritious 
matter continuous with that of the surface of the hemisphere. Along the 
inner edge of this eminence is seen a narrow white band, named corpus 
fimbriatum or tcenia hippocampi, which is prolonged from the fornix ; to the 
inner side of the tsenia is a part of the choroid plexus, and next to that the 
back of the optic thalamus. This cornu differs from the others in respect 
that it is not a mere cul-de-sac, but, by the mere separation of the mem- 
branes, can be made to communicate in its whole length with the surface 
of the brain by the fissure through which the choroid plexus enters. 



Fig. 372. 



Fig. 372. A DEEP VIEW OP 
THE LATERAL VENTRICLES 
AND THEIR CoRNUA WITH THR 
VELUM INTERPOSITUM. | 

The fornix has heen divided 
near its anterior pillars and 
turned back, c, the anterior 
part of the corpus callosum 
divided; e, the lyra on the 
lower surface of the corpus 
callosum and fornix ; /, ante- 
rior pillars of the fornix divided 
(these are represented of too 
large a size) ; g, anterior, and 
7t, posterior cornu of the lateral 
ventricle ; k, k, corpora striata; 
, pes hippocampi in the lower 
part of the middle cornu ; r, r t 
thalami optici ; s, , tsenia se- 
micircularis ; t, t, choroid 
plexus ; v, velum interpositum; 
a:, x, posterior pillars of the 
fornix ; y t emiuentia collate- 
ralis. 



The posterior cornu pro- 
jects backwards into the 
substance of the posterior 
lobe. At its extremity it 

is pointed, and directed inwards. On the inner side of its floor is a curved 
and pointed longitudinal eminence, named hippocampus minor, ergot, or 
calcar avis ; and at the junction of the posterior with the descending cornu, 
between the hippocampus major and minor, is a smooth eminence, named 
eminentia collateralis, or pes accessorius. 

The hippocampus minor is only the convex side of the fold which forms 
the calcarine sulcus, and part of the sulcus of the hippocampi ; and in like 




THE SEPTUM LUCIDUM. THE FORXIX. 545 

manner the eminentia collaterals corresponds with the posterior branch of 
the fissure of Sylvius. 

As some discussion has recently taken place in this country with regard to the 
value of the presence of the hippocampus minor in man, as a distinctive character of 
the human brain, it may be well to mention that this structure has been found even 
in the brains of quadrumana which do not belong to the highest group. In the 
human subject the posterior cornu varies greatly in size, and the hippocampus minor 
is still more variable in its development, being sometimes scarcely to be recognised, 
and at others proportionally large. It is usually most developed where the posterior 
cornu is longest ; but length of the posterior cornu, and prominence of the hip- 
pocampus minor, by no means occur in proportion to the dimensions of the hemi- 
sphere, but rather seem to be associated with thinness of both the medullary and 
the cortical substance. 

The septum lucidum is a thin translucent partition, placed between the 
two lateral ventricles. It extends vertically between the corpus callosum 
above, and the anterior part of the fornix below ; and, as the latter sinks 
down in front away from the corpus callosum, the septum is deep before 
and narrow behind. Anteriorly it lies in the hollow of the bend of the 
corpus callosum, in front of the fornix. 

The septum lucidum is double, being composed of two distinct laminse, 
having an interval between them, which contains fluid and is lined 
by an epitheliated membrane. This is the fifth ventricle, ventricle of the 
septum, or Sylvian ventricle. 

Each of the laminse of the septum which form the sides of the fifth ven- 
tricle, consists of an internal layer of white substance and an external layer 
of grey matter. 

In the human embryo, and also in some animals, the cavity of this ventricle com- 
municates with that of the third ventricle in front and below : but in the adult human 
brain it forms a separate and insulated cavity. Tarin described a small fissure in it 
between the pillars of the fornix ; but this is unusual. In disease it is sometimes 
distended with fluid. 

The fornix is an arched sheet of white longitudinal fibres, which appears 
partly in the floor of both lateral ventricles. It consists of two lateral 
halves, which are separated from each other in front and behind, but 
between those points are joined together in the mesial plane. The two 
parts in front form the anterior pillars of the fornix ; the middle conjoined 
part is named the body ; and the hind parts, which are again separated from 
each other, form the posterior pillars. 

The body of the fornix is triangular in shape, being broad and flattened 
behind, where it is connected with the under surface of the corpus callosum, 
and narrower in front as it dips down to leave that body, the space 
between them being filled up by the septum lucidum. Its lateral edges 
are in contact with the choroid plexuses, and its under surface rests upon 
the velum interpositum. 

The anterior crura or pillars of the fornix, cylindrical in form, descend, 
slightly apart from each other, through a quantity of grey matter on the 
sides of the third ventricle, between the corpora striata ; and, curving back- 
wards as they descend, reach the corpora albicantia. There each crus turns 
upon itself, making a twisted loop which forms the white portion of the 
corpus albicans of its own side, and ascends to enter the substance of the 
optic thalamus. These crura are connected with the peduncles of the pineal 
gland, and with the tsenia semicircularis, as will be afterwards described. 



546 



THE CEREBRUM. 



Immediately behind the anterior pillars, where they descend, the fornix, 
which further back rests upon the optic thalami, the velum interpositum 
alone intervening, has an interval on each side left between it and the 
groove where the optic thalamus and corpus striatum meet. This interval 
leads from the lateral ventricle to the third ventricle the space between the 
thalami and beneath the velum interpositum. The openings of opposite 
sides, passing downwards and backwards, meet in the middle line below, 
and thus is produced a passage, single below, but dividing into two 
branches above somewhat like the letter Y, and forming a communication 
between the third ventricle and both lateral ventricles. This passage is 
named the foramen of Monro, or foramen commune anterius. 



Fig. 373. 



Fig. 373, A. LOWER AND BACK PART OF THE 
CEREBRUM OP THE LEFT SIDE, SHOWING THE 
POSTERIOR AND MIDDLE CORNUA OP THE 
LATERAL VENTRICLE OPENED (altered from 
Hirschfeld and Leveille). | 

1, 1', inner convolution of the temporal lobe 
turning round into the convolution of the gyrus 
fornicatus, and showing on its surface the 
reticulated structure; 2, cut surface of the 
cerebral hemisphere ; 3, point of the posterior 
cornu of the lateral ventricle ; 3', eminentia 
collaterals ; 4, cut surface of the lower and 
back part of the corpus callosum divided near 
the middle ; 4', placed on the extension of the 
corpus callosum into the cerebral hemisphere, 
points by a line to the hippocampus minor in 
the posterior cornu ; 5, cut edge of the posterior 
pillar of the fornix passing down at 5', into 
the hippocampus major and corpus fimbriatum ; 
6, continuation of the corpus fimbriatum or 
taenia hippocampi ; 6', pes hippocampi ; 7, fascia 
dentata on the inside of the white substance of 
the tfenia. 

Fig. 373, B. SECTION OP THE HIPPOCAMPUS 
MAJOR TO snow THE ARRANGEMENT OP THE 
GREY AND WHITE SUBSTANCE (from Mayo). 

a, white layer on the surface of the hippo- 
campus ; b, grey substance which is involuted 
from the surface of the neighbouring convolution ; 
c, fascia dentata ; d, white reticulated substance 
of the lower part of the gyrus fornicatus; 
e, cavity of the lateral ventricle. 



The posterior crura or pillars of the 
fornix are the diverging continuations 
backwards of the two flat lateral bands 
of which the body is composed. At 

first they adhere to the under surface of the corpus callosum, then curving 
outwards, each crus enters the descending cornu of the corresponding 
lateral ventricle, and is prolonged as a narrow band of white matter, named 
tcenia hippocampi or corpus fimbriatum, which is situated on the inner 
margin of the hippocampus major, and extends to the extremity of that 
structure. 

On examining the under surface of the fornix and corpus callosum, there are 
seen posteriorly the thickened border or pad, and in front of it the diverging 




TRANSVERSE FISSURE OF THE CEREBRUM. 



547 



halves of the fornix, between which a triangular portion of the corpus 
callosum appears, marked with transverse, longitudinal, and oblique lines. 
To this part the term lyra has been applied. 

The transverse fissure of the cerebrum is the passage by which the pia 
mater passes from the surface into the ventricles of the brain to form the 
choroid plexus. It may be laid open in its whole extent, after the lateral 
ventricles have been opened, by completely dividing the fornix and corpus 
callosum in the middle line, and raising the divided parts from the undis- 
turbed velum interpositum below. It will then be found that, in like manner, 
the posterior and middle lobes of the brain, including the hippocampus 
major and corpus fimbriatum, may be raised from the subjacent parts as far 
as the extremity of the descending cornu of the lateral ventricle. The 
transverse fissure is, therefore, a fissure extending from the extremity of the 



Fig. 374. 




Fig. 374. VIEW OP THE UPPER SURFACE OP THE VELUM INTERPOSITTJM, CHOROID PLEXTJS, 
AND CORPORA STRIATA (from Sappey after Vicq-d'Azyr). f 

1, fore part of the tela choroidea or velum interpositum ; 2, choroid plexus; 3, left 
vein of Galen partly covered by the right ; 4, small veins from the front of the corpus 
callosum and the septum lucidum ; 5, veins from the corpus striatum ; 6, convoluted 
marginal vein of the choroid plexus ; 7, vein rising from the thalamus opticus and corpus 
striatum ; 8, vein proceeding from the inferior cornu and hippocampus major ; 9, one 
from the posterior cornu ; 10, anterior pillars of the fornix divided in front of the 
foramen of Monro ; 11, fornix divided near its forepart and turned backwards ; 12, lyra; 
13, posterior pillar united with, 14, the corpus callosum behind, and covered by the 
choroid plexus as it descends into the inferior cornu. 



548 THE CEREBRUM. 

descending cornu on one side, over the constricted part of the cerebrum, to 
the extremity of the descending cornu of the other side. It is bounded 
above by the corpus callosum and fornix in the middle, and more externally 
on each side by a free margin of the hemisphere : inferiorly it is bounded 
near the middle line by the corpora quadrigemina, and on each side by the 
cms cerebri and posterior part of the optic thalamus. 

In the free margin of the hemisphere brought into view by opening out the 
part of the transverse fissure which leads into the descending coruu of the 
lateral ventricle, there are seen (1st) the ribbon-like ledge formed by the 
corpus fiinbriatmn, internally to the hippocampus major ; (2nd) beneath 
this, a small grey indented ridge, the fascia dentata ; and (3rd) beneath the 
fascia dentata, the gyrus hippocampi. On making a transverse section, it is 
seen that the corpus fimbriatum is the free margin of the white substance of 
the hemisphere, and that the fascia dentata is the free margin of the cortical 
substance, and is continuous with the grey matter of the hippocampus 
major, and that thus the hippocampus major is the swelling in reverse of 
the sulcus between the fascia dentata and gyrus hippocampi. The fascia 
dentata can be traced up to the pad or bourrelet : its upper part is free of 
dentations, and is sometimes named fasciola cinerea. The dentations cor- 
respond with blood-vessels passing to and from the choroid plexus. 

The velum interpositum or tela choroidea, the membrane which connects 
the choroid plexuses of the two sides together, is a prolongation of the pia 
mater through the transverse fissure. It corresponds in extent with the 
fornix, which rests upon its upper surface ; and its more highly vascular 
free borders, projecting into the lateral ventricles, form the choroid plexuses. 

The choroid plexuses appear like two knotted fringes, reaching from 
the foramen of Monro, where they meet together beneath the fornix, to the 
point of each descending cornu. They consist of a highly vascular villous 
membrane. The villi with which they are covered are again divided upon 
their surfaces and at their borders into small processes, along which fine 
vessels are seen to run, Numerous small vessels pass between the plexuses 
and the surface of the corpora striata, as well as other neighbouring parts, and 
the epithelium of the ventricles is continued over their surface. Thus it is 
only at the foramen of Monro that the epithelial lining of the lateral ven- 
tricles is continuous with that of the third ventricle. 

The epithelium changes its character where it covers the plexus. It is there 
composed of large spheroidal corpuscles, in each of which is seen, besides a distinct 
nucleus, several yellowish granules, and one or more dark round oil-drops. According 
to Henle each of these cells is provided with short, slender, acuminate, transparent, 
and colourless processes. 

On raising the velum interpositum, two slight vascular fringes are seen 
running along its under surface, and diverging from each other behind. 
They form the choroid plexuses of the third ventricle. 

The choroid artery enters the velum mterpositum at the point of the 
descending cornu ; and other arteries enter from behind, beneath the corpus 
callosum. The greater number of the veins terminate in two principal 
vessels named the veins of Galen, which run backwards on the velum mter- 
positum, and passing out beneath the corpus callosum pour their blood into 
the straight sinus, having generally first united into a single trunk. 

Bichat supposed that the arachnoid membrane entered the third ventricle in the 
form of a tubular process, which passed beneath the posterior end of the corpus 
callosum and fornix, through the velum interpositum, and thus opened into the 



PARTS SEEN IX THE LATERAL VENTRICLES. 



549 



upper and back part of the third ventricle. 
canal of Bichat, is no longer admitted. 



The existence of this canal, named the 



The velum having been removed, the optic thalami are brought fully into 
view, together with the cavity of the third ventricle situated between 
them, while, behind the third ventricle, between it and the upper surface of 



375. 




Pig. 375. DISSECTION OF THE BRAIN FROM ABOVE, EXPOSING THE LATERAL, THIRD AND 
FOURTH VENTRICLES, WITH THE SURROUNDING PARTS (from Hirschfeld and Leveille). 

a, the anterior part or knee of the corpus callosum divided ; its fibres are seen spreading 
on each side into the cerebral hemispheres ; b, anterior part of the surface of the right 
corpus striatum in the anterior cornu of the lateral ventricle ; b', the same on the left 
side, in which the grey substance has been dissected so as to show the peduncular medul- 
lary fibres spi-eading through the corpus striatum into the cerebral hemisphere ; c, points 
by a line to the tzenia semicircularis : d, surface of the thalamus opticus ; e, the anterior 
pillars of the fornix divided; below they are seen descending in front of the third ven- 
tricle, and between them is seen a part of the anterior commissure ; above the letter 
is seen the fifth ventricle represented as a slit between the two laminae of the septum 
lucidum ;_/", placed on the soft or middle commissure ; g, in the posterior part of the third 
ventricle; on either side of this letter is the v/hite stria or peduncle of the pineal gland ; 
immediately below the letter is the small posterior commissure and the pineal gland ; h, 
the upper, and t, the lower of the corpora quadrigemina ; k, processus a cerebello ad 
cerebrum ; and close to this the valve of Vieussens, which is partly divided by a median 
incision along with the middle lobe of the cerebellum, so as to open up the fourth ven- 
tricle ; I, the hippocampus major and corpus fimbriatum separated from the posterior 
pillar of the fornix and descending into the middle cornu of the lateral ventricle ; m, 
posterior cornu of the lateral ventricle and hippocampus minor ; n, eminentia collateralis ; 
o, the cavity of the fourth ventricle ; p, posterior surface of the medulla oblongata ; r, 
section of the middle lobe showing the arbor vitse ; s, upper surface of the cerebellum 
brought into view on the left side by the removal of a considerable part of the posterior 
cerebral lobe. 



550 THE CEREBRUM. 

the cerebellum, are seen the pineal body, the corpora quadrigemina, the 
valve of Vieussens, and the processus a cerebello ad cerebrum. 

The THIRD VENTRICLE is a narrow longitudinal cleft placed between the 
optic thalami, which bound it on its two sides. It is covered above by the 
velum interpositum and the fornix. Beneath, its floor is formed by the 
following parts, which have been already described as seen on the base of 
the cerebrum ; viz., commencing from behind, the posterior perforated space, 
the corpora albicantia, the tuber ciuereum and infundibulum, and the 
lamina cinerea, the last of which also serves to close it in front, as high as 
the anterior commissure. Behind, is the anterior opening of the aqueduct 
of Sylvius. The cavity is crossed by three commissures, named from their 
position, anterior, middle, and posterior. 

The middle or soft commissure is composed almost entirely of grey 
matter, and connects the two thalami. It is variable in size, and some- 
times wanting ; it is frequently torn across in examining the brain. 

The anterior commissure is a round bundle of white fibres, placed imme- 
diately in front of the anterior pillars of the fornix, and crossing between the 
corpora striata. It marks the anterior boundary of the ventricle ; its fibres 
extend laterally through the corpora striata, a long way into the substance 
of the cerebral hemispheres.. 

The posterior commissure, also white but of smaller size, is placed across 
the back part of the ventricle, immediately before and below the pineal 
body, with which and with the corpora quadrigemina it is intimately 
connected. 

The corpora striata, situated in front and to the outer side of the optic 
thalami, are two large ovoid masses of grey matter, the greater part of each of 
which is embedded in the middle of the white substance of the hemisphere 
of the brain, whilst a part comes to the surface in the body and 
anterior cornu of the lateral ventricle. This intraventricular portion of 
the corpus striatum is of a pyriform shape, its larger end being turned 
forwards, and its narrow end being directed outwards and backwards, so 
that the optic thalami of the two sides are received between the diverging 
corpora striata. On cutting into it, there may be seen at some depth from 
the surface white fibres, which are prolonged from the corresponding cerebral 
peduncle, and give it the streaked appearance from which it has received its 
name. 

The extraventricular portion of the corpora striata will be afterwards 
described. 

Along the inner border of each corpus striatum, and in a depression 
between it and the optic thalamus, is seen a narrow whitish semitrans- 
parent band, named tcenia semicircularis, which continues backwards into 
the descending cornu of the ventricle, where its connections have not been 
determined with precision. In front it reaches the corresponding, anterior 
pillar of the fornix, and descends in connection with that cord of white 
substance. 

It is more transparent and firm on the surface, especially at its fore part : and 
this superficial stratum has been named stria cornea. The taenia consists of longi- 
tudinal white fibres, the deepest of which, running between the corpus striatum and 
the thalamus, were named by Vieussens centrum geminum semicircular e. Beneath 
it are one or two large veins, which receive those from the surface of the corpus 
Btriatum and end in the veins of the choroid plexuses. 

The thalami optici (posterior ganglia of the brain) are of an oval shape, 



THE THALAMI OPTICI. 



551 



and rest on the corresponding cerebral crura, which they in a manner 
embrace. On the outer side each thalamus is bounded by the corpus 
striatum and tsenia semicircularis. The upper surface, which is white, is 
free and prominent, and is partly seen in the lateral ventricle, and partly 
covered by the fornix. The part which is seen in the lateral ventricle is 
more elevated than the rest, and is named the anterior tubercle. The 
posterior surface, which is also white and free, projects into the descending 

Fig. 376. 




Fig. 



376. EIGHT HALF OF THE ENCEPHALIC PEDUNCLE AND CEREBELLUM AS 
FKOJI THE INSIDE IN A MEDIAN SECTION (after Reichert). 



II, right optic nerve ; II', optic commissure divided ; III, right third nerve ; VI, 
sixth nerve ; V 3, third ventricle ; Th, hack part of the thalamus options ; H, section of 
the pituitary body ; A. corpus albicans ; P, pineal gland ; c a, points by a lower line to 
the anterior commissure divided, and by an upper line to the divided anterior pillar of 
the fornix ; Ic, lamina cinerea ; i, infundibulum (cavity); tc, tuber cinereum ; /, mark 
of the anterior pillar of the fornix descending in the wall of the third ventricle ; c m, 
commissnra mollis ; sp, stria pinealis ; cp, posterior commissure, above it the peduncle 
of the pineal gland, and below it the upper end of the passage to the fourth ventricle ; 
Q, corpora quadrigemina (section); as, aqueduct of Sylvius near the fourth ventricle ; 
P V, pons Varolii divided in the middle ; M, medulla oblongata ; p a, right anterior 
pyramid; pel, decussating bands cut across ; pp, posterior pyramids; c, central canal 
with grey substance surrounding it divided. In the cerebellum, av, stem of white sub- 
stance in the centre of the middle lobe of the cerebellum, ramifying towards the arbor 
vitaa ; s v, superior vermiform process or vertical portion of the middle lobe ; s c, single 
folium, which passes across between the posterior superior lobes; c', the folia, which 
unite the posterior inferior lobes ; p, pyramid ; u, uvula ; n, nodule ; 1, part of the 
laminae of the square lobe ; 2, posterior superior lobe ; 3, posterior inferior lobe ; 4, lob ul us 
gracilis ; 5, bi ventral lobe ; 6, amygdaloid lobe. 



cornu of the lateral ventricle. The inner sides of the two thalami are in 
contact one with the other. They present the grey substance of the inte- 
rior of the thalami uncovered with white, and are generally partially united 
together by a transverse portion, which forms the middle or soft commissure 
of the third ventricle. 



552 THE CEREBRUM. 

The pineal body or gland (conarium) is a small reddish body, which is 
placed beneath the back part of the corpus callosum, and rests upon the 
anterior elevations of the corpora quadrigemina. It is attached to the under 
surface of the velum interpositum, so that it is liable to be torn away from 
the brain in removing that membrane. It is about the size of a small 
cherry-stone. Its base of attachment, which is its broader part, is directed 
forwards, and is connected with the rest of the cerebrum by white substance. 
This white substance is principally collected into two small rounded 
bundles, named peduncles of the pineal gland, which pass forwards upon 
the optic thalami along their upper and inner borders, and may be 
traced as far as the anterior pillars of the fornix, in conjunction with which 
they descend. These peduncles are connected with each other behind, and 
the band of union between them is adherent to the back of the posterior 
commissure. 

This band is represented by Reichert as folding forwards and then backwards, so 
as to leave a hollow, which he calls recessus pinealis, opening backwards above the 
pineal body. Some anatomists have described two inferior peduncles, which descend 
upon the inner surface of the thalami. 

The pineal gland is very vascular. It is hollowed out into two or more 
cells, which, sometimes at least, open anteriorly into the ventricle, and 
almost always contain, besides a viscid fluid, a quantity of gritty matter, 
named acervulus cerebri. This consists of microscopic round particles, 
aggregated into small compound masses, which are again collected into 
larger groups. It is composed of the so-called amylaceous or amyloid 
bodies, and of earthy salts combined with animal matter, viz., phosphate 
and carbonate of lime, with a little phosphate of magnesia and ammonia 
(Stromeyer). It is found at all ages, frequently in young children, and 
sometimes even in the foetus. It cannot, therefore, be regarded as the 
product of disease. 

This sabulous matter is frequently found on the outside of the pineal body, or 
even deposited upon its peduncles. It is found also in the choroid plexuses ; and 
scattered corpora amylacea occur in other parts of the membranes of the brain. 
Huschke has pointed out that the pineal body is larger in the child and the female 
than in the adult male. In the brains of other mammals it is proportionally larger 
than in the human subject, and less loaded with the matter of acervulus cerebri. 

The corpora or tubercular quadrigemina are four rounded eminences, 
separated by a crucial depression, and placed two on each side of the middle 
line, one before another. They are connected with the back of the optic 
thalami, and with the cerebral peduncles at either side ; and they are 
placed above the passage leading from the third to the fourth ventricle. 

The upper or anterior tubercles are somewhat larger and darker in colour 
than the posterior. In the adult, both pairs are solid, and are composed of 
white substance on the surface, and of grey matter within. 

They receive bands of white fibres from below, the majority of which are 
derived from a fasciculus named the fillet. A white cord also passes up 
on each side from the cerebellum to the corpora quadrigemina, and is 
continued onwards to the thalami : these two white cords are the pro- 
cessus a cerebello ad cerebrum, or superior peduncles of the cerebellum. At 
each side of the corpora quadragemina there proceed outwards two white 
bands, which pass to the thalami and to the commencements of the optic 
tracts. These bands are prominent on the surface, and are sometimes named 
brachia. 



DEEP PARTS OF THE CEREBRUM. 553 

In the human brain the quadrigeminal bodies are small in comparison 
with those of animals. In ruoainant, soliped, aud rodent animals, the 

Fig. 377. 




To, 



Fig. 377. VIEW OP THE MEDULLA OBLONGATA, PONS VAROLII, CRURA CEREBRI, AND 
CENTRAL PARTS OF THE ENCEPHALON FROM THE RIGHT SIDE. 

The corpus striatum and thalamus opticus have been preserved in connection with the 
central lobe and crura cerebri, while the remainder of the cerebrum has been removed. 

St, upper surface of the corpus striatum ; Th, back part of the thalamus opticus ; G, 
placed on the middle of the five or six convolutions constituting the central lobe or island 
of Reil, the cerebral substance being removed from its circumference ; Sy, fissure of 
Sylvius, from which these convolutions radiate, and in which are seen the white striae of 
the olfactory tract ; I, the olfactory tract divided and hanging down from the groove in 
the convolution which lodges it ; II, optic nerves a little way in front of the commissure ; 
a, right corpus albicans with the tuber cinereum and infundibulum in front of it ; h, 
hypophysis or pituitary body ; e, external, and i, internal corpus geniculatum at the back 
part of the optic tract; P, peduncle or crus of the cerebrum ; /, fillet; III, right oculo- 
motor nerve ; p, pineal gland ; q, corpora quadrigemina ; IV, trochlear nerve rising from 
-y, the valve of Vieussens ; V, placed on the pons Varolii above the right nervus trige- 
minus ; s, the superior, wi, the middle, aud in, the inferior peduncles of the crus cere- 
belli cut short ; VI, the sixth nerve ; VII a, facial nerve ; VII b, auditory nerve ; on 
the medulla oblongata the parts are indicated as follows : VIII, placed opposite to the 
cut end of the pneumo-gastric nerve ; a, the glosso-pharyngeal ; and b, the uppermost 
fibres of the spinal accessory nerve ; IX, the hypoglossal nerve ; p a, anterior pyramid ; 
o, olivary body; a r, arciform fibres; p p, posterior pyramid; r, restiform body; tr, 
eminence corresponding to the tubercle of Rolando ; at the commencement of the spinal 
cord, ca, indicates the anterior, cp, the posterior, and cl, the lateral columns; C I, 
anterior and posterior roots of the suboccipital or first cervical nerve. 

o o 



554 THE CEREBRUM. 

anterior tubercles are much larger than the posterior, as may be seen in the 
sheep, horse, and rabbit ; and hence the name nates, formerly applied to 
the anterior, and tebtes to the posterior tubercles. In the brains of carnivora, 
the posterior tubercles are rather the larger. In the foetus of man and 
mammals these eminences are at first single on each side, and have 
an internal cavity communicating with the ventricles. They are constant 
in the brains of all vertebrate animals ; but in fishes, reptiles, and birds, 
in which animals they receive the name of optic lobes, they are only two in 
number, and hollow : in marsupialia and monotremata, they are also two in 
number, but are solid. 

Optic tracts and corpora, geidculata. The optic tracts, which have already 
been referred to in connection with the base of the cerebrum, are attached 
to and embrace the under side of the corresponding peduncles, and 
may be traced back to the thalami. Ench tract, somewhat cylindrical 
towards the optic commissure, becomes flattened and broader as it approaches 
the thalamus, and makes a bend as it turns round the peduncle to reach 
the back part of that body. Near this bend, which is named the knee 
(genu), and to the outer side of the corpora quadrigemina, are placed two 
small oblong and flattened eminences connected with the posterior extremity 
of the optic tract. They are two little masses of grey matter about the size 
and shape of coffee-beans, placed one on the outer and one on the inner side 
of the genu of the optic tract, and hence are named respectively corpus 
geniculatum externum and internum. They send fibres into the optic tract 
and also into the thalamns of the same side. 

The fibres of the optic tracts are therefore derived from three sources, 
viz. , the thalamus, the tubercula quadrigemina, and the corpora geniculata. 

The processus a cerebello ad cerebrum are two large white cords extending 
downwards and somewhat outwards from the corpora qnadrigemina to the 
fore part of the cerebellum, and connecting the latter with the cerebrum. 
They rest upon the crura cerebri, to which they are united, and between 
them is the valve of Vieussens. 

The valve of Vieussens (velum medullare anterius), stretched between the 
processus a cerebello ad cerebrum, is a thin layer of nervous matter, which 
lies over the passage from the third to the fourth ventricle, and, lower down, 
covers in a part of the fourth ventricle itself. It is narrow above, where it 
is connected with the quadrigeminal bodies, and broader below, where it 
is continuous with the median portion of the cerebellum. 

The upper portion of the valve is composed of white substance, but a few 
transverse ridges of grey matter extend upon its lower half, as if they were 
prolonged from the grey lamellae of the cerebellum with which the valve is there 
continuous. From between the posterior quadrigeminal tubercles a slight 
median ridge, named frmnulum, descends a little way upon the valve ; 
and on the sides of this the commencing fibres of the fourth pair of 
nerves pass transversely outwards. The back part of the valve is over- 
lapped and concealed by the superior vermiform process of the cerebellum. 



INTERNAL STRUCTURE OF THE CEREBRUM. 

The cerebrum, like the rest of the encephalon, is composed of white and grey 
substance, the white pervading nearly the whole of its extent, though more exclu- 
sively composing its deeper parts ; the grey forming a covering of some thickness over 



STRUCTURE OF THE FIBROUS SUBSTANCE. 555 

the whole surface of the convolutions, and collected in distinct masses in certain of 
the deeper part, such as the corpora striata, thalami optici, corpora quadrigemina, 
and crura cerebri. To the grey substance, the names of cineritious and cortical have 
been applied ; to the white that of medullary. 

1. The white matter of the encephalon consists of tubular fibres, in general still 
smaller than those of the cord, and more prone to become varicose. The general 
direction which these follow is best seen in a brain that has been hardened by 
immersion in alcohol, although it is true that in an ordinary dissection of such 
hardened masses with the scalpel, we do not then trace the single fibres, but only 
the smaller bundles and fibrous lamellae which they form by their aggregation. It must 
also be admitted that were they intimately decussate, the tearing of fibres across is 
liable to be mistaken for the separation of sets of fibres one from the other ; and it 
is necessary to correct such errors by the examination of sections under the micro- 
scope. The microscopic examination of the cerebrum, however, is as yet still less 

Fig. 378. 




Fig. 378. SKETCH OP A DISSECTION SHOWING THE CONNECTION OP THR COLUMNS OP THE 
MEDULLA OBLONGATA WITH THE CEREBRUM AND CEREBELLUM (from Mayo), i 

In the lower part of the figure the medulla oblongata is entire where it is prolonged 
downwards into the spinal cord ; a, the anterior pyramid ; a', its continuation upwards 
into the pons Varolii (m) ; c, olivary body ; cf, olivary fasciculus ; behind c', the fasciculi 
teretes are represented ; d, the white laminae in part of the cerebellum ; /, superior 
peduncle of the cerebellum ; y, anterior part or crust of the cerebral peduncle ; h, part 
of the fibres radiating from the peduncle into the right cerebral hemisphere, of which a 
considerable extent is shown containing parts of the anterior, middle, and posterior lobes ; 
Ji, y, y, part of the corona radiata ; h' (in front), central fibres of the convolutions ; i, 
fillet; I, back of the thalamus opticus ; m, pons Varolii; n, inferior peduncle of the 
crus cerebelli ; o, section of the pes hippocampi ; r, tegmentum ; y, y, show the white 
fibres issuing from the corpus striatum. 

complete than that of the spinal marrow and medulla oblongata. By the dissection 
of artificially prepared brains, aided in part by microscopic observation, the following 
general facts have been ascertained. 

The fibres of the cerebrum, though exceedingly complicated in their arrange- 
ment, and forming many different groups, may be referred to three principal 
systems, according to the general course which they take, viz. : 1. Ascending or 

o o 2 



556 



THE CEREBRUM. 



peduncular fibres, which pass up from the medulla oblongata to the hemispheres, 
and constitute the peduncles of the cerebrum. These fibres increase in number as 
they ascend through the pons, and still further in passing through the optic thalami 
and striated bodies, beyond which they spread in all directions into the hemispheres. 

2. Transverse or commissural fibres, which connect the two hemispheres together. 

3. Longitudinal or collateral fibres, which, keeping on the same side of the middle 
line, connect more or less distant parts of the same hemisphere. 

1. In each hemisphere the peduncular fibres consist of a main body and of certain 
accessory bundles of fibres. 

The main body is derived from the anterior pyramid, from the fasciculi teretes, 
and from the posterior pyramid. After it has passed through the pons, and be- 
come increased in amount, it is separated into two parts in the crus cerebri by a 
layer of dark cineritious matter, named locus niger. The lower or superficial part, 
which is derived from the pyramid, consist almost entirely of white fibres, col- 
lected into coarse fasciculi, and is named the crust or basis, or the fasciculated por- 
tion of the peduncle (Foville). The upper part, composed principally of the fasci- 
culus teres and posterior pyramid, is named the tegmentum. It is softer and finer in 
texture, and is mixed with much grey matter. 

Still increasing in number within the peduncle, these two sets of fibres ascend to 
the thalamus and corpus striatum. A much larger number of fibres diverging 



Fig. 370. Fig. 379. POSTERIOR VIEW 

OK THE PEDUNCLES OF TUN 
CEREBRUM AND CEREBEL- 
LUM (after Arnold). f 

The lower and fore part of 
the cerebral hemispheres is 
preserved, the cerebellum is 
completely detached from its 
peduncles, and on the right 
side the corpora quadrigemina 
and thalamus opticus have 
been dissected, a, fasciculus 
teres of the left side ; b, fibres 
of the tegmentum ascending 
through the right thalaraus ; 

c, left corpora quadrigemina ; 

d, lateral column of the cord ; 

e, restiform body ; /, superior 
peduncles of the cerebellum ; 
g, fibres of the crust ; i, ?', 
the fillets ; k, k, corpora 
stria ta ; Z, the left thalamus ; 
m, m, sections of the middle 
peduncles of the cerebellum ; 
n, section of the left inferior 
peduncle ; p, left postei'ior 
pyramid ; g, section of the 
corpus callosum ; s, under 

surface of the same, and below it the cavity of the fifth ventricle ; e, left anterior pillar 
of the fornix; y, decussation of the radiating fibres with the crossing fibres of the corpus 
callosum. 




from these bodies appear to pass to the medullary substance of the hemispheres ; but 
the actual continuity of the individual fibres spreading out in the hemisphere with 
those ascending to the thalamus and corpus striatum is doubted by many authors, 
and among them, by Kolliker. 

The assemblage of radiating fibres in each hemisphere might be compared to a 
fan, bent into the form of an incomplete hollow cone, having its concave surface 
turned downwards and outwards ; hence the name corona radiata applied to them 
by Reil, and fibrous cone by Mayo. 



TRANSVERSE AND COLLATERAL FIBRES. 



557 



The accessory fibres of the peduncular system are as follows : 

a. The superior peduncles of the cerebellum, (processus ad cerebrum,) which are 
continued up beneath the corpora quadrigernina, and form part of the tegmentum. 

b. The bundle of fibres on each side, named the fillet (lemniscus). This, which is 
originally derived from the anterior column of the cord, proceeds from the olivary 
fasciculus of the medulla oblongata, as previously described. Reinforced by fibres 
from the corpus dentatum of the olivary body, it ascends through the back part of 
the pons, still increasing in size. Appearing at the side of the cerebral peduncle, 
above the upper border of the pons, it divides into two portions, of which one crosses 
over the superior peduncle of the cerebellum to the corpora quadrigemina, meeting 
its fellow of the opposite side; while the other is continued upwards with the fibres 
of the tegmentum. 

c. Other fibres accessory to the peduncles take their rise in the grey matter of the 
corpora quadrigemina (the brachia], and proceed on to the thalami. 

d. Lastly, fibres of another set, having a similar destination, are derived from the 
corpora geuiculata. 

2. The transverse commissural, or connecting fibres of the cerebrum, include the 
following sets. 
a. The cross fibres of the corpus callosum pass laterally into the substance of 



Fig. 380. 



Fig. 380. VIEW OF A DISSECTION OF TUB 
FIBRES IN THE LEFT CEREBRAL HEMI- 
SPHERE FROM BELOW (after Mayo). | 

The most of the middle lobe in its lower 
part has been removed. , the anterior and 
', the posterior part of the fillet of the 
corpus callosum ; b; g, section of the cms 
cerebri ; b, tegmentum ; y, crust separated 
from the last by the locus niger ; c', fibres 
stretching from the back part of the corpus 
callosum into the posterior lobe ; e, fasciculus 
uncinatus connecting the anterior and middle 
lubes across the Sylvian fissure ; /, /, trans- 
verse fibres from the corpus callosum passing 
into the cerebral hemispheres ; I, back part 
of the thalamus ; m, corpus albicans ; q, 
median section of the corpus callosum ; ;*, 
radiating fibres of the hemispheres ; t, ante- 
rior pillar of the fornix descending into the 
corpus albicans (m) ; v, collateral fibres of 
the convolutions ; x , anterior commissure. 



the hemispheres, some being directed up- 
wards, whilst others spread outwards on 
the roof of the lateral ventricles, forming 
there what is named the tapetum. Having 
intersected the peduncular radiating fibres, 
they spread out into the hemispheres, 
reaching everywhere the grey matter of the 
convolutions. 

b. The fibres of the anterior commissure 

pass laterally into the corpora striata, and bending backwards, extend a long way 
into the middle of the hemispheres, on each side. 

c. The fibres of the posterior commissure run through the optic thalami, and are 
soon lost in the substance of the hemispheres outside these bodies. 

3. The third system of fibres in the cerebrum, the longitudinal or collateral, in- 
cludes those of the fornix, tsenia semicircularis, and striae lougitudinales of the 
corpus callosum, already sufficiently described ; and likewise the following. 

a. Fibres of the yyrus fornicatus ; fillet of the corpus callosum (Mayo). These 
fibres constitute the white substance of the gyms fornicatus, and take a longitudinal 
course immediately above the transverse fibres of the corpus callosum. In front 




558 THE CEREBRUM. 

they bend downwards within the gyms to which they belong, and are connected 
with the anterior perforated space, being joined by certain longitudinal fibres which 
run along the under surface of the corpus callosum near the middle line, passing 
near and upon the upper edge of the septum lucidum. Behind, they turn round the 
back of the corpus callosum and thence descend to the point of the middle lobe, where, 
according to Foville, they again reach the perforated space. Offsets from these fibres 
pass upwards and backwards into the secondary convolutions derived from the gyrus 
fornicatus in the longitudinal fissure. 

b. fasciculus uncinat,us. Under this name is described a white bundle, seen on 
the lower aspect of the hemisphere, passing across the bottom of the Sylvian fissure, 
and connecting the anterior with the middle and posterior lobes. The fibres of this 
bundle expand at each extremity, and the more superficial of them are curved or 
hooked sharply between the contiguous parts of the anterior and middle lobes, 
whence it has derived its name. 

c. The convolutions of the cerebrum are connected with each other by white 
fibres, which lie immediately beneath the cortical substance. Some of them pass 
across the bottom of the suicus between adjacent convolutions ; whilst others, which 
are longer and run deeper, connect convolutions situated at a greater distance from 
one another. 

Fig. 381. 




Fig. 381. VIEW OP A DISSECTION OP THE FIBRES OF THE GYROS FORNIOATUS AND FORNIX, 
IN THE RIGHT HEMISPHERE ^sli^htiy altered from Foville). 4 

A, the anterior lobe ; B, the posterior lobe ; a, a', a", fibres of the gyrus fornicatus ; 
C, cf, oblique bands of fibres of some of its accessory gyri; b, tegtnentum, and g, crust of 
the crus cerebri, separated by the locus niger ; I, thalamus ; m, fissure of Sylvius ; n, corpus 
albicans ; q, median section of the corpus callosum ; s, septum lucidum ; t, the fornix, 
its anterior pillar descending into the corpus albicans, and then emerging from that at its 
termination (*) in the thalarnus ; 1, the olfactory bulb ; 2, the optic commissure. 

The researches of Foville have led him to differ considerably from other 
anatomists as to the course of the fibres of the cerebrum, as will be seen from the 
following statement of his views. 

1. The crust or fasciculated portion of each cerebral peduncle, derived from the 
anterior pyramid, forms by itself the peduncular fibrous cone, and is thence con- 
tinued on into the radiating fibres of the cerebrum, which are destined only for the 
convolutions on the convex surface of the hemisphere, including the outer half of 
the marginal convolution of the longitudinal fissure, and the inner half of the con- 
volution of the Sylvian fissure. 

2. The fibres of the tegmentum, having entered the thalamus, pass on in two ways 
no part of them, however, joining the radiating peduncular fibres. 

a. One set pass upwards through the thalamus and corpus -triatum, above which 



FIBROUS STRUCTURE. FOVILLE'S VIEWS. 



559 



they then turn inwards, and, joining with those of the opposite side, form the trans- 
verse fibres of the corpus callosum. The corpus callosum is therefore regarded as 
a commissure of the cerebral peduncles only none of its cross fibres spreading into 
the convolutions, as is generally believed. 

b. The second set of fibres of the tegmentum, corresponding with the fasciculi 
teretes and part of the posterior pyramids, run forwards near the middle line, along 
the under side of the third ventricle and corpus striatum, through the grey matter 
in front of the pons, to the anterior perforated space. The remaining part of the 
posterior pyramid forms the taenia semicircularis, which, passing down in front of the 
anterior pillar of the fornix, also reaches the perforated space. From this space 
more fibres are reflected upwards on the sides of the corpus striatum to join the 
corpus callosum. 

3. As dependencies of the posterior peduncular fibres, and connected with them at 
the borders of the anterior perforated space, are : 

a. Several sets of longitudinal arched fibres, which embrace, in a series of rings, 
the radiating peduncular system. These are the deep fibres of the taenia semicircu- 
laris a somewhat similar baud beneath the outer part of the corpus striatum the 
half of the fornix with the corpus fimbriatum the longitudinal fibres placed on the 
upper and under surface of the corpus callosum, and those of the septum lucidum ; 
and, lastly, two remarkable systems of longitudinal fibres one constituting the 
entire white substance of the gyrus fornicatus (from end to end), also of its accessory 
convolutions, and of the inner half of the marginal convolution of the longitudinal 
fissure ; and the other, forming the white substance of the convolutions of the island 
of lieil, and the adjoining half of the convolution of the Sylvian fissure. None of 
the parts just named receive fibres from the radiating peduncular set. 

6. In connection with this system is a thin stratum of white fibres, found upon the 
internal surface of the ventricles, aud prolonged through the transverse fissure into 
the reticulated white substance covering the lower end of the gyrus fornicatus ; 
whence, according to Foville, it extends, as an exceedingly thin layer of medullary 
matter, all over the cortical substance of the hemisphere. 

c. The anterior commissure does not reach the convolutions, but radiates upon the 
outer sides of the corpora striata and thalami. 

II. The fjrvij matter on the convoluted surface of the cerebrum is divided into two. 
and in some regions into three strata, by interposed thin layers of white substance. 
In examining it from without inwards, we meet with 1. A thin coating of white 
matter situated on the surface, which on a section appears as a faint white line, 
bounding the grey surface externally. This superficial white layer is not equally 



Fig. 382. SECTION OP Fig. 382. 

THE COKTICAL SlJB- 
STANCE OF A CEREBKAL 

CONVOLUTION (from 
Remak). 

In A, the parts are 
nearly of the natural 
size. To the right of the 
figure, a and e are two 
white, and b and / two 
grey strata ; to the left 
of the figure, an addi- 
tional whi^e layer, ^di- 
vides the first grey into 
two, b and d. In B, a 
small part of the cortical 
substance of a con volution 
is represented, magnified 
to show more clearly the 

relative position of the strata ; a, superficial white layer ; 6, reddish grey layer ; c, inter- 
mediate white layer; d, inner part of the outer grey layer ; e, thin white layer; /, inner 
grey layer ; g, radiatiug white fibres from the medullary substance of the convolution 
passing into the layers of the cortical substance. 




560 



THE CEREBRUM. 



thick over all parts of the cortical substance, but becomes thicker as it approaches 
the borders of the convoluted surface ; it is accordingly less conspicuous on the 
lateral convex aspect of the hemispheres, and more so on tho convolutions situated in 
the longitudinal fissure which approach the white surface of the corpus callosum, and 
on those of the under surface of the brain. It is especially well marked on the 
middle lobe, near the descending cornu of the lateral ventricle, where the convo- 
luted surface is bounded by the posterior pillar of the fornix, and it has been there 
described under the name of the reticulated wliite, substance. It consists of remark- 
ably fine tubular fibres, for the most part varicose, which run parallel with the sur- 
face of the convolutions, but intersect each other in various directions. The ter- 
mination and connections of these fibres are unknown. This superficial white layer 
contains also a few small cells with processes, and an abundant granular matrix. 
2. Immediately beneath the white layer just described, is found a comparatively thick 
layer of grey or reddish grey matter, the colour of which, as indeed of the grey sub- 
stance generally, is deeper or lighter according as its very numerous vessels contain 
much or little blood. Then follow, 3. Another thin whitish layer; and 4. A thin 
grey stratum. This last lies next to the central white matter of the hemisphere. 
Remak considers it as similar in nature to the gelatinous substance of the spinal 
cord. According to this account, the cortical substance consists of two layers of grey 
substance, and two of white ; but in several convolutions, especially those situated 
near the corpus callosum, a third white stratum may be seen, which divides the 
most superficial grey layer into two, thus making six in all, namely, three grey and 
three white. 

Fig. 3 S3. 




Fig. 383. MINUTE STKUCTUKK OF THE CEREBRAL SUBSTAKO ; (from Kolliker), MAGNIFIED 

220 DIAMETERS. 

A, cells and structural elements from the inner part of the cortical substance of the 
cerebral convolutions ; a, larger cells, chiefly from the middle grey layer, showing a 
variable number of radiating processes; b, smaller cells from the more superficial grey 
layer, in part belonging to connective tissue; c, a nerve-fibre with its axis-filament 
partly exposed. 

B, finest nerve-fibres from the superficial wliite layer of the cortical substance of a 
convolution, some showing the varicose condition. 



The cortical grey substance consists of nerve-cells of rather variable size, which are 
angular, fusiform, round, or oval in shape, and for the most part caudate, and lie in a 
granular matrix; also of small nucleus-like vesicles, which resemble those seen in 
the cortical substance of the cerebellum, and, according to Todd, are here also 
collected into a special stratum. In the middle grey layer, the cells are of variable 
gize, some being so small as to resemble nuclei ; but others of much larger dimen- 
sions are abundant, and, according to Kolliker, present from one to six processes. 



CORTICAL AND INTERNAL GREY SUBSTANCES. 561 

In the innermost grey layer the cells have similar characters, but often contain 
pigmentary matter. Tubular fibres exist throughout : those of one set run parallel 
with the surface, and at certain depths are more densely aggregated, so as to form 
the before-mentioned white layers : they are also present in the intervening grey 
strata, but there they are wider apart. The manner in which they begin and end is 
not known ; it seems not improbable, however, that they are dependencies of the 
commissural system of fibres. These stratified fibres, if they might be so called, are 
intersected by another set of tubular fibres, which come from the central white 
mass of the hemispheres, and run perpendicularly through the cortical substance, 
becoming finer and spreading more out from each other as they approach the surface. 
The further disposition of these central or perpendicular fibres is uncertain; 
Yalentin describes them as forming terminal loops or arches, but this is denied by 
Remak and Hannover. Remak states that they gradually disappear from view at 
different depths, as they pass through the successive layers, the last of them vanish- 
ing in the superficial grey stratum ; but he is unable to say positively how they 
terminate. It sometimes seemed to him as if the last of them, after intersecting the 
fibres of the deeper white stratum, became continuous with those of the outermost 
layer ; but of this he by no means speaks confidently. Hannover maintains that 
the perpendicular fibres are connected at their extremities with the nerve-cells in the 
cortical substance. 

The grey matter of the lamina cinerea, tuber cinereum, and posterior perforated 
spot, appears both in the base of the brain and in the floor of the third ventricle. 
The lamina cinerea is connected externally with the grey matter of the anterior 
perforated spot, and from that point a continuity of grey matter can be traced to 
the swelling of the olfactory bulb. Thus also continuity is established between the 
grey matter of the hemispheres and that of the interior of the brain. 

III. The grey matter of the interior of the cerebrum may be examined in the series 
of its deposits from behind forwards. 

In the crura cerebri, the grey matter is collected into a dark mass, the locus 
niger, which lies between the crust and the tegmentum, and is also diffused among 
the fasciculi of the tegmentum ; below this it is continuous with that of the pons 
and medulla oblongata, and through them with that of the spinal cord, as has already 
been sufficiently described. In the upper part of each tegmentum is a round reddish 
grey centre, the red centre of Stilling, the superior olive of Luys. 

In the centre of each of the corpora quadrigemina grey matter is also found ; and 
this collection is stated by Huschke to be continuous below with the posterior cornu 
of the grey matter of the spinal cord, posteriorly with that of the corpus dentatum 
of the cerebellum, and anteriorly with the soft commissure, the septum lucidum, 
optic thalami, and corpus callosum. Grey matter occurs also in the pineal gland, 
and in the corpora geniculata. These last bodies appear to be_ appendages of the 
optic thalami. 

The grey matter of the optic thalamus constitutes the principal bulk of that body ; 
it is, however, partially divided into an inner and an outer portion, by white fibres 
passing through it. 

The corpus striatum contains three grey centres. That which forms the intra- 
ventricular portion of the body, and is connected inferiorly with the lamina cinerea, 
and with that portion of the grey matter of the optic thalamus which is seen in the 
third ventricle, is named the nucleus caudatus. The principal centre of the extra- 
ventricular portion, named nucleus lenticularis, external and inferior to the nucleus 
caudatus, is separated from that centre by the white substance of the fibrous cone, 
which, as it passes outwards, appears, when cut across, as a broad white band extend- 
ing from behind forwards, and traversed by striae of grey matter passing from one 
centre to the other. Between the nucleus lenticularis and the island of Reil, which 
lies opposite to it, there intervenes a thin lamelliform deposit of grey matter, the 
nucleus tceniceformis (Arnold), or claustruin (Burdach), which, in a transverse section, 
is seen as a thin line. The lenticular nucleus is continuous with the grey matter of 
the anterior perforated space. 

The corpus striatum and optic thalamus contain cells very much like those of the 
cortical substance. In the corpora quadrigemina there are larger cells, approaching 
in size to those of the cerebellum, besides very small cells and nucleiform bodies. 
The dark matter, forming the so-called locus niger of the cerebral peduncles, and 



562 



CEREBRO-SPINAL MEMBRANES. 



that in the floor of the fourth ventricle, contain caudate cells, many of them of the 
largest size, with long appendages, and deeply coloured with pigment. (Hannover, 
Rech. Microscop. sur le Systeme Nerveux. Copenhagen, 1844). 

The pineal body, like the pituitary body, has already been sufficiently described. 
The deep connection of some of the cranial nerves with the basal parts of the cere- 
brum, as well as that of others with the remaining portions of the encephalon, will 
be referred to in the description of these nerves. 



THE MEMBRANES OF THE BRAIN AND SPINAL CORD. 

The cerebro-spinal axis is protected by three membranes, named also 
meninges. They are : 1. Au external fibrous membrane, named the dura 
mater, which closely lines the interior of the skull, and forms a loose sheath 
in the spinal canal ; 2. An internal areolo-vascular tunic, the pia mater, 
which accurately covers the brain and spinal cord ; and 3. An intermediate 
serous sac, the arachnoid membrane, wLich, by its parietal and visceral 
layers, covers the internal surface of the dura mater on the one hand, and 
is reflected over the pia mater on the other. 



THE DURA MATER. 



The dura mater, a very strong dense inelastic fibrous tunic of considerable 
thickness, is closely lined on its inner surface by the outer poition of the 

Fig. 384. 




Fig. 384. THE CRANIUM OPENED TO snow THE FALX OP THE CEREBRUM, AND TENTORIUM 
OF THE CEREBELLUM. 4 

a, right side of the falx cerebri ; a', its anterior narrow part attached to the crista 
galli ; 6, tentorium cerebelli of the right side, united to the base of the falx cerebri 
from 2 to 3, in the Hue of the straight sinus, and attached to the superior border 
of the petrous bone between 3 and 3' ; b', aperture between the right and left divisions 
of the tentorium for the isthmus cerebri ; 1, 1, the superior longitudinal sinus; 2, 2, the 
inferior ; 3, 3, the lateral sinus; 3, 3', the superior petrosal sinus j 3', is close to the 
anterior clinoid process. 



DUEA MATER. FALX.-TEXTOKIUM. 563 

arachnoid, and with it, therefore, forms a fibro-serous membrane, which is 
free, smooth, and epitheliated on its inner surface, where it is turned 
towards the brain and cord, but which, by its outer surface, is connected 
with the surrounding parts, in a somewhat different manner in the cranium 
and in the spinal canal. 

The outer surface of the cranial portion adheres to the inner surface of 
the bones, and forms their internal periosteum. The connection between 
the two depends, in a great measure, on blood-vessels and small fibrous 
processes, which pass from one to the other ; and the dura mater, when 
detached and allowed to float in water, presents a flocculent appearance on 
its outer surface, iu consequence of the torn parts projecting from it. The 
adhesion between the membrane and the bone is more intimate opposite 
the sutures, and also generally at the base of the skull, which is uneven, 
and perforated by numerous foramina, through which the dura mater is 
prolonged to the outer surface, being there continuous with the pericranium. 
The fibrous tissue of the dura mater becomes blended with the areolar 
sheaths of the nerves, at the foramina which give issue to them. 

In leaving the skull, the dura mater is intimately attached to the margin 
of the foramen magnum ; but within the vertebral canal it forms a loose 
sheath around the cord (#ieca), and is not adherent to the bones, which 
have an independent periosteum. Towards the lower end of the canal, a 
few fibrous slips proceed from the outer surface of the dura mater to be 
fixed to the vertebrae. The space intervening between the wall of the 
canal and the dura mater is occupied by loose fat, by watery areolar tissue, 
and by a plexus of spinal veins. 

Opposite each iutervertebral foramen the dura-matral theca presents two 
openings, placed side by side, which give passage to the two roots of the 
correspond! Lg spinal nerve. It is continued as a tubular prolongation on, 
the nerve, and is lost in its sheath. Besides this, it is connected with 
the circumference of the foramen by areolar tissue. 

The fibrous tissue of the dura mater, especially within the skull, is divi- 
sible into two distinct layers, and at various places these layers separate 
from each other and leave intervening channels, called sinuses. These 
sinuses, which have been elsewhere described, are canals for venous blood, 
and are lined with a continuation of the internal membrane of the veins. 

The dura mater also sends inwards into the cavity of the skull three 
strong membranous processes, or partitions^ formed by duplication of its 
inner layer. Of these, one descends vertically in the median plane, and is 
received into the longitudinal fissure between the two hemispheres of the 
cerebrum. This is thj falx cerebri. The second is an arched or vaulted 
partition, stretched across the back part of the skull, between the cerebrum 
and the cerebellum ; it is n amed the tentorium cerebelli. Below this, another 
vertical partition, named falx cerebelli, of small extent, passes down between 
the hemispheres of the cerebellum. 

The /ate cerebri is narrow in front, where it is fixed to the crista galli, 
and broader behind, where it is attached to the middle of the upper surface 
of the tentorium, along which line of attachment the straight sinus is 
situated. Along its upper convex border, which is attached above to the 
middle line of the inner surface of the cranium, runs the supeiior longi- 
tudinal sinus. Its under edge is free, and reaches to within a short distance 
of the corpus callosum, approaching nearer to it behind. This border con- 
tains the inferior longitudinal sinus. 

The tentorium, or tent, is elevated in the middle, and declines downwards 



564 CEREBRO-SPINAL MEMBRANES. 

in all directions towards its circumference, thus corresponding in form with 
the upper surface of the cerebellum. Its inner border is free and concave, and 
leaves in front of it an oval opening, through which the isthmus encephali 
descends. It is attached behind and at the sides by its convex border to 
the horizontal part of the crucial ridges of the occipital bone, and there 
encloses the lateral sinuses. Farther forward it is connected with the upper 
edge of the petrous portion of the temporal bone the superior petrosal 
fcinus running along this line of attachment. At the point of the pars 
petrosa, the external and internal borders meet, and may be said to inter- 
sect each other the former being then continued inwards to the posterior, 
and the latter forwards to the anterior clinoid process. 

The falx cercbelli (falx minor) descends from the middle of the posterior 
border of the tentorium with which it is connected, along the vertical ridge 
named the internal occipital crest, towards the foramen magnum, bifurcating 
there into two smaller folds. Its attachment to the bony ridge marks the 
course of the posterior occipital siuus, or sinuses. 

Structure. The dura mater consists of -white fibrous and elastic tissue, arranged in 
bands and laminae, crossing each other. It is traversed by numerous blood-vessels 
which are chiefly destined for the bones. Minute nervous filaments, derived from 
the fourth, fifth, and eighth cranial nerves, and from the sympathetic, are described 
as entering the dura mater of the brain. Nervous filaments have likewise been 
traced in the dura mater of the spinal column. (Luschka and Riidinger, quoted by 
Hyrtl.) 

THE PIA MATER. 

The pia mater is a delicate, fibrous, and highly vascular membrane, 
which immediately invests the brain and spinal cord. 

Upoii the hemispheres of the brain it is applied to the entire cortical 
surface of the convolutions, and dips into all the sulci. From its internal 
surface very numerous small vessels enter the grey matter and extend for 
some distance perpendicularly into the substance of the brain. The inner 
surface of the cerebral pia mater is on this account very flocculent, and is 
named tomentum ceiebri. On the cerebellum a similar arrangement exists, 
but the membrane is finer and the vessels from its inner surface are not so 
long. The pia mater is also prolonged into the ventiicles, and there forms 
the velum interpositum and choroid plexus. 

Structure. The pia mater consists of interlaced bundles of areolar tissue, con- 
veying great numbers of blood-vessels ; and, indeed, its peculiar office, both on the 
brain and spinal cord, seems to be that of providing a nidus or matrix for the 
support of the blood-vessels, as these are subdivided before they enter the nervous 
substance. According to Fohmann and Arnold, it contains numerous lymphatic 
vessels. Purkinje describes a i etiform arrangement of nervous fibrils, derived, accord- 
ing to Kolliker and others, from the sympathetic, the third, sixth, facial, pneumo- 
gastric. and accessory nerves. 

On the spinal cord the pia mater has a very different structure from that 
which it presents on the encephalon, so that it has even been described by 
Home as a different membrane under the name neurilcmma of Hie cord. It 
is thicker, firmer, less vascular, and more adherent to the subjacent nervous 
matter : its greater strength is owing to its containing fibrous tissue, which 
is arranged in longitudinal shining bundles. A reduplication of this mem- 
brane dips down into the anterior fissure of the cord, and serves to conduct 
blood-vessels into that part. A thinner process passes into the greater part 
of the posterior fissure. At the roots of the nerves, both in the spine and 



SUBARACHXOID SPACE AXD FLUID. 565 

in the cranium, the pia mater becomes continuous with the neurilemma. It 
is supplied with nerves from the sympathetic. 

Towards the upper part of the cord, the pia mater presents a greyish 
mottled appearance, which is owing to pigment particles deposited within 
its tissue. 

THE ARACHNOID MEMBRANE. 

The arachnoid is a very fine delicate serous membrane, which, like other 
membranes of thab class, forms the lining boundary of a shut sac. The 
walls of this sac consist of two portions, one of which, a distinct membrane 
on the surface of the pia mater, is the visceral or cerebral layer of the 
arachnoid, while the other, giving the smooth surfaca presented by the dura 
mater on its interior, is described by some anatomists as the parietal layer 
of the arachnoid, while, according to the view taken by others, it is merely 
the serous surface of the dura mater. 

The parietal wall of the arachnoid space is invested with a layer of polygonal 
epithelial cells, which are flattened and nucleated. Besides this, it presents 
in the greater part of its extent no tissue distinct from the dura mater ; and 
hence it is that Koiliker and others object to the term parietal layer of 
the arachnoid membrane as applied to the structure of this surface. It may 
be mentioned, however, that in certain recesses, as for example at the sides 
of the crista galli, and between the trabeculse into which the deep fibres of 
the dura mater are thrown in the neighbourhood of the superior longitudinal 
sinns, a small amount of delicate connective tissue beneath the epithelium 
may be distinguished from the dense fibres of the dura mater. 

The visceral layer of the arachnoid is a distinct transparent membrane 
which passes over the various eminences and depressions on the cerebrum 
and cerebellum, without dipping into the sulci and smaller fissures ; nor is 
it uniformly and closely adherent to the pia mater. The interval left 
between the arachnoid membrane and pia mater is named generally the 
subarachnoid space. 

This subarachnoid space is wider and more evident in some positions than 
in others. Thus, in the longitudinal fissure, the arachnoid does not descend 
to the bottom, but passes across, immediately below the edge of the falx, at 
a little distance above the corpus callosum. In the interval thus left, the 
arteries of the corpus callosum run backwards along that body. At the 
base of the brain and in the spinal canal there is a wide interval between 
the arachnoid and the pia mater. In the base of the brain, this subarachnoid 
space extends in front over the pons and the interpeduncular recess as far 
forwards as the optic nerves, and behind it forms a considerable interval 
between the cerebellum and the back of the medulla oblongata. In the 
spinal canal it surrounds the cord, forming a space of considerable extent. 

A certain quantity of fluid is contained between the arachnoid membrane 
and the dura mater ; but it has been shown by Magendie that the chief part 
of the cerebro-spinal fluid is lodged under the arachnoid, in the subarachnoid 
space. 

Magendie also pointed out the existence of a sort of septum dividing the 
spinal subarachnoid space at the back of the cord. This is a thin mem- 
branous partition, which passes in the median plane from the pia mater 
covering the posterior median fissure of the cord to the opposite part of the 
loose portion of the arachnoid membrane. It is incomplete and cribriform ; 
and consists of bundles of white fibres interlaced more or less with one 
another. Fibrous bands of the same texture pass across the subarachnoid 




566 CEREBRO-SPINAL MEMBRANES. 

space in various situations both within the spinal canal and at the base of 
the brain, stretching thus from the arachnoid membrane to the pia mater. 

Fig. 385. TRANSVERSE SECTION OF THE SPINAL 
CORD AND ITS ENVELOPES (from Sappey after 
Hirschfeld and Leveille). 

1, dura mater or tbeca ; 2, parietal layer of 
the arachnoid membrane: 3, internal or loose 
.arachnoid ; 4 and 7, snbarachnoid cavity or 
space ; 5, hinder part of the antero-lateral 
column; 6, space between the arachnoid and the 
dura mater, or between the inner and outer folds 
of the arachnoid membrane : 8, reflection of the 
one fold into the other; 9, sheath furnished to the spinal nerve by the dura mater; 10, 
posterior ganglionic root; 11, smaller anterior root; 12, section of the ligamentum 
denticulatum. This figure does not show the septum which posteriorly divides the 
subarachnoid space into right and left parts : this would be placed between the arachnoid 
at 3, and the pia mater covering the posterior surface of the cord. 

As the cerebral and spinal nerves proceed to their foramina of exit from 
within the dura mater, they are loosely surrounded by tubular sheaths of 
the arachnoid membrane, which extend along each nerve from the visceral 
to the parietal layer. 

Structure. When examined under the microscope, the visceral or true arach- 
noid is found to consist of very distinctly separated riband-like bundles of fibrous 
tissue interlaced with one another, and a simple layer of scaly epithelium on the 
surface. Volkmann has described a rich plexus of nerves in the arachnoid mem- 
brane of certain ruminants. Kolliker has failed to detect their presence ; but they 
have been again described by Bochdalek, who traces them to the portio minor of the 
fifth, the facial, and accessorius nerves; and they have likewise been followed by 
Luschka. 

Cerebro-spinal fluid. This is a very limpid serous fluid, which occupies the sub- 
arachnoid space. When collected immediately after death, its quantity was found 
by Magendie in the human subject to vary from two drachms to two ounces. It is 
slightly alkaline, and consists, according to an analysis by Lassaigne, of 98 '5 parts 
of water, the remaining 1 '5 per cent, being solid matter, animal and saline. In 
experiments made on the dog, it was found by Magendie to be reproduced in thirty- 
six hours, after it had been drawn off by puncturing the membranes at the lower 
part of the cord. When pressure is made upon the brain, the quantity of fluid in the 
spinal subarachnoid space is increased, and conversely, it may be forced from the 
spinal cavity upwards into the cranium. 

Ligamentum denticulatum. This is a narrow fibrous band which runs along 
each side of the spinal cord in the subarachnoid space, between the anterior 
and posterior roots of the nerves, commencing above at the foramen mag- 
num, and reaching down to the lower pointed end of the cord. By its 
inner edge this band is connected with the pia mater of the cord, while its 
outer margin is widely denticulated ; and its denticulations, traversing the 
arachnoid space, with the arachnoid membrane reflected over them, are 
attached by their points to the inner surface of the dura mater, and thus 
serve to support the cord along the sides and to maintain it in the middle 
of the cavity. The first or highest denticulation is fixed opposite the 
margin of the foramen magnum, between the vertebral artery and the 
hypoglossal nerve ; and the others follow in order, alternating with the 
successive pairs of spinal nerves. In all, there are about twenty-two of 
these points of insertion. At the lower end, the ligamentum denticulatum 



GLAKDUL2E PACCHIOXI. -BLOOD-VESSELS. 567 

may be regarded as continued into the terminal filament of the spinal 
cord, which thus connects it to the dura mater at the lower end of the 
sheath. (See Figures 341 and 342.) 

Structure, It consists of white fibrous tissue, mixed with many exceedingly fine 
elastic fibres which are seen on applying acetic acid. It is obviously continuous 
on the one hand with the fibrous tissue of the pia mater, and on the other with that 
of the dura mater. 

The pia mater of the cord presents a conspicuous fibrous band, running 
down in front over the anterior median fissure. This was named by Haller, 
linea splendens. 

Glandules Pacchioni. Upon the external surface of the dura mater, in 
the vicinity of the longitudinal sinus, are seen numerous small pulpy-looking 
elevations, generally collected into clusters, named glands of Pacchioni. 
The inner surface of the calvarium is marked by little pits, which receive 
these eminences. Similar excrescences are seen on the internal surface of 
the dura mater, and upon the pia mater on each side of the longitudinal 
sinus, and also projecting into the interior of that sinus. Occasionally they 
are found also in other situations. 

These bodies are not found at birth ; and according to the brothers 
Wenzel, they exist only in very small number, if at all, before the third year. 
After the seventh year they are usually found, and they increase in number 
greatly as life advances ; in some cases, however, they are altogether want- 
ing. In animals there appears to be no corresponding structure. 

On a careful examination of the connections of these bodies it will be 
found that the elevations, found on the outer surface of the dura mater and 
within the longitudinal sinus, in no instance take origin in those positions, 
but that they are grape-like bodies which are attached more deeply, and in 
their growth have perforated the dura mater. Their precise origin and nature 
were long the subject of conflicting opinions, but it has been satisfactorily 
shown by Luschka that they are only an enlarged condition of normal villi 
of the arachnoid, and that no other structure is involved in their formation. 
Their most prolific source is, as one may very soon discover, the cerebral or 
generally acknowledged layer of the arachnoid, but they likewise arise in a 
similar manner from the serous surface of the dura mater, and may some- 
times be found of all sizes in the recesses into which that surface is thrown 
in the neighbourhood of the longitudinal sinus. (Luschka, in Miiller's 
Archiv. 1852 ; and " Die Adergeflechte des Menschlichen Gehirns," 1855. 
See also Cleland " On Tumours of the Dura Mater, &c.," in the Glasgow 
Medical Journal, 1863.) 

BLOOD- VESSELS OF THE BRAIN AND SPINAL CORD. 

The origin and course of these vessels have already been described in the 
Section Angeiology. In passing to their distribution the several arteries, 
having passed across the arachnoid cavity, enter the subarachnoid space an I 
then divide and subdivide into branches, which, in their farther ramification 
in the nervous centres, are supported by the pia mater, and, it may be 
remarked, are more deeply placed in the various fissures and sulci than the 
small veins, which do not accompany the arteries, but pursue a different 
course and are seen upon the surface of the pia mater. 

Moreover, it is to be observed that, whilst the main branches of the 
arteries are situated at the base of the brain, the principal veins tend 



568 



SIZE AND WEIGHT OF THE BRAIN. 



towards the upper surface of the hemispheres, where they enter the superior 
and inferior longitudinal sinuses : the veins of Galen, however, coming 
from the lateral ventricles and choroid plexuses, run backwards to the 
straight sinus. 



SIZE AND WEIGHT OF THE ENCEPHALON. 

In the following table illustrating the average weight of the adult male and female 
brain, the results obtained by Sims, Clendinning, Tiedemann, and J. Reid have 
been brought together in such a form as to exhibit in groups the most commonly 
prevailing weight ; the numbers being also simplified by the omission of fractions. 
(Sims, " Medico-Chirurg. Trans.," vol. xix., pp. 3537; Clendinning, "Medico- 
Chirurg. Trans.," vol. xxi., pp. 59 68; Tiedemann, "Das Him des Negers," 
Heidelberg, 1837, pp. 6, 7; Reid, "London and Edinburgh Monthly Journal of 
Medical Science," April, 1843, p. 298, &c.) 

Table of the Average Weight of the Male amd Female Brain. 



MALES, aged 21 years and upwards. 


FEMALES, aged 21 years and upwards. 


> 


IS umber ot brains 
at each weight 
observed by 


1 




1 


Number of brains 
at each weight 
observed ty 


1 


Classification 


5 


' 






s^ -r- VMiiao&uva b&uu 

-^ into three 


eS 


'"" 




-s 


" . 


into three 


si 


a 




c 


groups 
fi 'S to show the 


*1 


* 




, 




It 
S'S 


groups, 
to show the 


gl 

bo 


1 

1 









g ^ prevailing 
weight. 




| 




1 




I * 

1 1 


prevailing 
ictight. 


1 


a 



a 


1 


s 1 

53 o 




1 





C/j 

a 


" 


3 i^ 









i 


H 


M 


H 






6 


a 


H 


tf p 1 




34 








_ 


1 1 > > 


31 





i 


1 


1 ^ 




37 





2 






2 


32 





i 





1 


a 


38 


1 










1 


rH 


35 










2 


oj / from ~i g 


39 
40 
4 1 
42 


2 


3 

2 

3 

4 


- 


1 
1 

2 


4 
3 

5 
8 


S r from ^ o 

X 1 1 o 

ji 3 \r hi 

I 45 oz. J jg 


36 
39 


i 


4 ! 

3 j 1 

3 1 


2 
2 


4 
6 
2 
6 


Si 31 oz. f c 

> <S \ 4. J- O 

o J to 1 - 
g \ 40 oz. J JG 

5 


43 





6 


2 


3 


11 


^ 


40 


3 


3 





4 


10 ; 




44 


1 


6 


2 


3 


12 


4 1 


2 


8 -- 


2 


12 >! 




45 
46 
47 
48 


6 
2 
2 
4 


8 
10 
6 
8 


2 


1 

8 
10 
11 


>C O 00 >O 
r-H CM rH 04 


* 
r from ^ g 


42 
43 

44 
45 


3 

6 
5 
4 


6 
4 
9 


1 




3 

7 
13 

7 


19 
20 


f from -\ ^ 
3 ' 41 oz. F 

*!l to ii 

<3 v. 47 oz. J > 


49 


3 


2 


2 


12 


19 


c J 46 OZ. f S 


46 


2 


9 2 


12 


25 






4 


4 


5 


13 


26 


i * I 


47 


2 


5 





7 


14 J 


s 


5! 


3 


3 


2 


19 


27 


S I. 53 oz. J ta 


48 





2 


2 


2 


6 ^ 




52 





5 


4 


6 


15 


p 


49 





1 


2 


7 


10 


00 


53 
54 

II 


4 
3 


2 

2 


4 
1 
2 
1 


10 
5 
4 

6 


20 
11 




50 

52 
53 


1 


1 


1 

2 


4 
4 


7 
6 


9 ( from "i 

,SJ 4802. F| 

J to f C 

Si 5 6oz. Js 


57 
58 





1 


4 


o 
2 


7 


1C ? ro ^ II 


54 
56 i 


2 
1 





2 
1 x 


P 


59 
60 
61 


- 


1 


2 
2 


3 
1 
1 


; m -vr j-| 

J hg (. 6 5 oz. J j 


Tot. 30 + 72+12 + 77=191 








62 








T 


i S 






63 











1 


i 1 






6q 





1 ~ 


i ; 






Tot. 35 + 78 + 39 + 126 = 278. 



According to this table, the maximum weight of the adult male brain, in a series of 
278 cases, was 65 oz., and the minimum weight 34 oz. In a series of 191 cases, the 
maximum weight of the adult female brain was 56 oz., and the minimum 31 oz. ; the 
difference between the extreme weights in the male subject being no less than 31 oz., 
and in the female 25 oz. By grouping the cases together in the manner indicated by 
brackets, it is shown that in a very large proportion the weight of the male brain 



TABLE OF THE WEIGHT OF THE BRAIN. 



569 



ranges between 46 oz. and 53 oz., and that of the female brain between 41 oz. and 
47 oz. The prevailing weights of the adult male and female brain may therefore be 
said to range between those terms ; and, by taking the mean, an average weight is 
deduced of 49| oz. for the male, and of 44 oz. for the female brain, results which 
correspond closely with the statements generally received. 

Although many female brains exceed in weight particular male brains, the general 
fact is sufficiently shown, that the adult male encephalon is heavier than that of the 
female, the average difference being from 5 to 6 oz. This general superiority in 
absolute weight of the male over the female brain has been ascertained to exist at 
every period of life. In new-born infants the brain was found by Tiedemann to weigh 
on an average from 14| oz. to 15| oz. in the male, and from 10 oz. to 131 oz. in the 
female : a fact of considerable interest in practical midwifery, for it has been shown 
that difficult labours occur in by far the largest number in the birth of male children . 
(Simpson, London and Edinburgh Monthly Journal of Medical Science, 1845.) 

With the above results the observations of Peacock, published in the " Monthly 
Journ. of Med. Science " for 1847, and further observations by the same author in the 
" Journ. of the Pathol. Soc." in 1860, in the main agree. 

The elaborate table compiled by Rudolph Wagner, and published in his " Yorstudien 
zu einer Wissensch. Morphol. und Physiol. des Menschl. Gehirns," 1860, containing 
964 recorded cases in which the weight of the brain had been ascertained, may also be 
referred to as another recent useful contribution to the knowledge of this subject. 

In illustration of the variation in the average weight of the brain at different ages 
the following table is given, deduced from the elaborate researches of Dr. Robert 
Boyd, in the examination of the brains of 2,086 sane persons of both sexes dying in the 
St. Marylebone Infirmary, and published in the Philos. Trans, for 1860. The weights 
are stated in oz. avoird. and decimal fractions of them. 



Table of the Weight of the Brain of Males and Females at different Ages. 



PERIODS OF LIFE. 


MALES. 


FEMALES. 


Number 
weighed. 


Maximum. 


EJ 

1 


Average. 


Average. 


9 


| 


Number 
weighed. 


1 Children prematurely still- 
born 


25 

43 
42 
16 
15 
46 

34 
29 
27 

22 
19 

59 
no 
J 37 
119 
127 

104 

24 


13.1 

22. 
15.37 
32.75 
30.75 
36.13 
41.25 
50.5 
49.5 
57.25 

58.5 
57. 
60.75 
60. 
59. 
59.5 

55.25 
53.75 


1.31 

9.37 
6. 
10.5 
1'>.75 
17.75 
23.25 
30.5 
24.5 
39.25 

36.5 
39.25 
33.75 
33.75 
30.5 
36.25 

37.75 
41. 


5.6 

13.87 
11.65 
17.42 
21.29 
27.42 
33.25 
38.71 
40.23 
45.96 

48.54 
47.9 
48.2 
47.75 
47.44 
46.4 

45.5 
45.34 


4.62 

12.25 
10. 
15.94 
19.76 
25.7 
29.8 
34.97 
40.11 
40.78 

43.94 
43.7 
43.09 
42.81 
43.12 
42.69 

41.27 

39.77 


1.29 

8. 
1.75 
11 
13. 
16.37 
18. 
27.75 
34.75 
34. 

37.5 
35.75 
33.25 
27.5 
36.25 
32.5 

29.25 
33.25 


9.13 

15.12 
16. 
32.5 
34.75 
39.13 
37. 
44.5 

25 



55.25 
53. 
52.5 
52.5 
54. 

49.5 

48. 


18 

3i 
39 

20 
25 
40 

33 
2 9 
19 
18 

16 
72 

8 9 
106 
103 
149 

148 

77 


2 Children still-born at full 
period 




4 Under 3 months 


5 From 3 to 6 months 


6 From 6 to 12 months 


7 From 1 to 2 years 


8 From 2 to 4 years 


9 From 4 to 7 years 
10 From 7 to 14 years 


11 From 14 to 20 years .. 


12 From 20 to 30 years 


13 From 30 to 40 years 
14 From 40 to 50 years 


15 From 50 to 60 years 
16 From 60 to 70 years 


17 From 70 to 80 years 
18 Upwards of 80 years 


be 1 Persons above 14 years 

^.5 
> ~ I Persons from 14 to 70 years . . 
< ) 


699 
57i 


58. 
59.12 


36.1 
35. 


47.1 

47.7 


42.5 
43.15 


33.1 
33.8 


52.1 
53.15 


760 
535 



Anatomists have differed considerably in their statements as to the period at which 
the brain attains its full size, and also as to the effect of old age in diminishing the 
weight of this organ. Soemmerring held that the brain reached its full size as early 

P P 



570 SIZE AND WEIGHT OF THE BRAIN. 

as the third year ; the Wenzels and Sir W. Hamilton fixed the period about the seventh , 
and Tiedemann between the seventh and eighth years. Gall and Spurzheim were 
of opinion that the brain continued to grow until the fortieth year. The observations 
of Sims, Tiedemann, and Eeid, appear to show that in both sexes the weight of 
the brain in general increases rapidly up to the seventh year, then more slowly to 
between sixteen and twenty, and again more slowly to between thirty-one and forty, 
at which time it reaches its maximum point. Beyond that period there appears a 
slow but progressive diminution in weight of about 1 oz. during each subsequent 
decennial period ; thus confirming the opinion that the brain diminishes in advanced 
life. According to Peacock, the maximum weight of the brain is attained between 
the ages of twenty and thirty years. The table of Boyd inserted above would appear 
to show a somewhat earlier period as that at which the maximum is reached in both 
sexes, and that the period of decline scarcely begins before sixty years. With this 
result the observations of Huschke, made upon the brains of 359 men and 245 women, 
in general agree. (" Schadel, Him, und Seele des Menschen und der Thiere, &c.," 
1854.) 

All other circumstances being alike, the size of the brain appears to bear a general 
relation to the mental power of the individual, although many instances occur in 
which this rule is not applicable. The brain of Cuvier weighed upwards of 64 oz., and 
there are other recorded examples of brains belonging to men of great talent which 
nearly equalled it in weight. (Emille Rousseau, " Maladie et autopsie de M. G. Cuvier," 
Lancette Franaise, Mai 26, 1832.) On the other hand, the brain in idiots is remark- 
ably small. In three idiots, whose ages were sixteen, forty, and fifty years, Tiedemann 
found the weight of their respective brains to be 19| oz., 25f oz., and 22^ oz; and 
Dr. Sims records the case of a female idiot twelve years old, whose brain weighed 
27 oz. Allen Thomson has found the brain of a dwarfish idiot girl seventeen years of 
age to weigh 18^ oz. after preservation in alcohol. 

The human brain is found to be absolutely heavier than that of all the lower 
animals except the elephant and whale. The brain of the elephant, according to 
Perrault, Moulins, and Sir A. Cooper, weighs between 8 and 10 Ibs. ; whilst that 
of the whale was found by Rudolphi, in a specimen 75 feet long, to weigh upwards 
of 5 Ibs. 

The relative weight of the encephalon to the body is liable to great variation; 
nevertheless, the facts to be gathered from the tables of Clendinning, Tiedemann, and 
Reid, furnish this interesting general result. In a series of 81 males, the average 
proportion between the weight of the brain and that of the body at the ages of twenty 
years and upwards, was found to be as 1 to 36*5 ; and in a series of 82 females, to be 
as 1 to 36 '46. In these cases, the deaths were the result of more or less prolonged 
disease; but in six previously healthy males, who died suddenly from disease or 
accident, the average proportion was 1 to 40 -8. 

The proportionate weight of the brain to that of the body is much greater at birth 
than at any other period of life, being, according to Tiedemann, about 1 to 5'85 in the 
male, and about 1 to 6 '5 in the female. From the observations already referred to, 
it further appears that the proportion diminishes gradually up to the tenth year, 
being then about 1 to 14. From the tenth to the twentieth year, the relative increase 
of the body is most striking, the ratio of the two being at the end of that period 
about Ito30. After the twentieth year, the general average of 1 to 36'5 prevails, 
with a further trifling decrease in advanced life. 

Viewed in relation to the weight of his body, the brain of man may be stated 
generally to be heavier than the brains of the lower animals ; but there are some 
exceptions to the rule, as in the case of certain species of small birds, in the smaller 
apes, and in some small rodent animals. 

The attempts hitherto made to measure or estimate the relative proportions of the 
different convoluted parts of the cerebrum to each other and to the degree of intelli- 
gence, either more directly or by the cranioscopic methods, have as yet been attended 
with little success. The more recent researches of Rudolph Wagner, which have been 
farther prosecuted by his son, hold out some promise when fully carried out to afford 
more definite results. 

These researches had for their object to institute an accurate comparison between 
the brains of certain persons of known intelligence, cultivation, and mental power, 
and those of persons of an ordinary or lower grade. As examples of brains of men of 



MEASUREMENT OF THE CONVOLUTIONS. 



571 



superior intellect, he selected those of Professor Gauss, a well-known mathematician 
of eminence, and Professor Fuchs, a clinical teacher ; and as examples of brains of 
ordinary persons, those of a woman of 29 and a workman named Krebs, all of which 
he examined and measured with scrupulous care. 

The general result of R. Wagner's researches upon these and other brains may be 
stated to be as follows. 1st. Although the greatest number of brains belonging to men 
of superior intellect are found to be heaviest or largest, yet there are so many instances 
in which the brains of such persons have not surpassed, or have even fallen below the 
average size of the brains of ordinary persons, that superiority of size cannot in the 
present state of our knowledge be regarded as a constant accompaniment of superiority 
of intellect, even when due regard has been paid to the comparative stature and other 
circumstances of the individuals. 

2nd. It would appear that, in the brains of certain persons of superior intellect, 
the cerebral convolutions have been found more numerous and more deeply 
divided than in those of persons of ordinary mental endowments and without culti- 
vation. But numerous exceptional instances are also found of paucity of convolutions 
coincident with superior intellect, which make it impossible at present to deduce any 
certain conclusion with respect to the relation between the number or extent of the 
convolutions and the intellectual manifestations in different persons. 

The careful measurement of all the convolutions and the intervening grooves in the 
four brains above mentioned has been carried out by the younger Wagner, and the 
tables and results of these measurements published by him as an appendix to his 
father's treatise. (Hermann Wagner, " Maasbestimmuugen der Oberflache des 
Grossen Gehirns," &c., Cassel und Gb'ttingen, 1864.) 

The following short table extracted from Hermann Wagner's memoir, and simplified 
by the omission of small fractions and by the reduction of the measurements from 
square millimetres to English square inches, may give the reader some idea of the 
nature of the inquiry. 

Comparative measurement of the extent of surface of the Convolutions of the 
Cerebrum and its lobes. 





Surface of each lobe separately. 


Free and deep 
surfaces of Cerebrum. 










Whole 








surface 
















of 




3 


1 


1 
'a 




1 


S|| 


Cerebrum. 




2 




8 




11 


la 








P, 




H 


<n M o oo 




1. Gauss 


139. 


70.6 


59.4 


68.4 


112.8 


228.2 


341. 


2. Fuchs 


143.4 


69.5 


59. 


67.5 


110.7 


231.3 


342. 


3. Woman 


130. 


65. 


51. 


66.8 


107.5 


209.9 


317.5 


4. Workman 


113.2 


62.3 


50.5 


62. 


97.4 


193.6 


291. 



WEIGHT OF THE SEVERAL PARTS OF THE ENCEPHALON. 

As the result of observations made in reference to this subject, on the brains of 53 
males and 34 females, between the ages of twenty -five and fifty -five, Dr. J. Reid has 
given the following table : 

Males. Females. Difference, 
oz. drs. oz. drs. oz. drs. 

Average weight of cerebrum . . . . 43 15f 38 12 5 3| 

cerebellum . . ..54 4 12 7f 

pons and medulla oblongata 15f 1 

entire encephalon .50 3^ 44 8| 511 

With these results the observations of Huschke, derived from a special examination 
of the brains of 22 females, and 38 males, mainly agree. 

p p 2 



572 "WEIGHT OF THE BBAIN AND SPINAL COED. 

From this it appears that the proportionate weight of the cerebellum to that of the 
cerebrum is, in the male, as 1 to 8f, and in the female as 1 to 8j. The cerebellum 
attains its maximum weight from the twenty -fifth to the fortieth year ; but the increase 
in weight after the fourteenth year is shown to be relatively greater in the female than 
in the male. The whole cerebellum apart from the pons and medulla is heavier in the 
male ; the lateral lobes of the cerebellum are also heavier in the male. In the male 
the vermiform process increases gradually from the twentieth to the fiftieth year ; in 
the female it remains stationary during that period, and after the fiftieth year 
diminishes rapidly. 

In the new-born infant the ratio of the weight of the cerebellum to that of the whole 
brain is strikingly different from that observed in the adult, being, according to 
Chaussier, between 1 to 13 and 1 to 26 ; by Cruveilhier it was found to be 1 to 20. 
Huschke found the weight of the cerebellum, medulla oblongata, and pons together 
in the new-born infant, as compared with that of the brain, to be in the proportion of 
1 to 15, and 1 to 13. In the adult, the proportions were 1 to 7, and 1 to 6. 

In most mammalia, the cerebellum is found to be heavier in proportion to the 
cerebrum, than it is in the human subject ; in other words, the cerebrum in man is 
larger in proportion to the cerebellum. 

Soemmerring pointed out the fact that the brain is larger in proportion to the 
nerves connected with it in man than in the lower animals. 

A comparison of the width of the cerebrum with that of the medulla oblongata 
shows that the proportionate diameter of the brain to that of the medulla oblongata 
is greater in man than in any animal, except the dolphin, in which creature, however, 
it must be remembered that the cerebral lobes exhibit a disproportionate lateral 
development. The width of the cerebrum in man, as compared with that of the 
medulla oblongata at its base or broadest part, is about 7 to 1, while in many quadru- 
l eds it is as 3 to 1 or even as 2 to 1. 

WEIGHT OF THE SPINAL CORD. 

Divested of its membranes and nerves, the spinal cord in the human subject weighs 
from 1 oz. to 1| oz, and therefore its proportion to the encephalon is about 1 to 33. 
Meckel states it as 1 to 40. 

The disproportion between the brain and the spinal cord becomes less and less in 
the descending scale of vertebrata, until at length, in cold-blooded animals, the 
spinal cord becomes heavier than the brain. Thus, in the mouse, the weight of 
the brain, in proportion to that of the spinal cord, is as 4 to 1 ; in the pigeon, as 3| 
t) 1 ; in the newt only as to 1 ; and in the lamprey, as ^ to 1. 

In comparison with the size of the body, the spinal cord in man may be stated in 
general terms to be much smaller than it is in animals. In regard to the cold- 
blooded animals, to birds, and to small mammalia, this has been actually demonstrated, 
but not in reference to the larger mammalia. 

R. Wagner states, as follows, the proportion of the weight of the spinal marrow 
taken as 1 to the encephalon and its parts 



a, to the nerve roots 

b, to the medulla and pons 

c, to the cerebellum 

d, to the cerebrum 

e, to the encephalon 



1 : 0-53 

1 : 1* 

1 : 5-18 

1 : 42-78 

1 : 48-96 



SPECIFIC GRAVITY OF THE ENCEPHALON. 

The specific gravity of different parts of the encephalon has of late attracted some 
attention from its having been observed that it varies to some extent in different 
kinds of disease. From the researches of Bucknill, Sankey, Aitken, and Peacock, it 
appears that the average specific gravity of the whole encephalon is about 1036, that 
of the grey matter 1034, and that of the white 1040. There are also considerable 
differences in the specific gravity of some of the internal parts. (William Aitken, 
" The Science and Practice of Medicine," 1865, vol. 2, p. 265 : J. C. Bucknill in " The 
Lancet," 1852 : Sankey, in the "Brit, and For. Med. Chir. Eeview," 1853 : Thos. B. 
Peacock, in the Trans, of the Patliol. Soc. of London, 1861-2.) 



PRIMITIVE CEREBRO-SPIXAL CAXAL. 



573 



DEVELOPMENT OF THE CEREBRO-SPINAL AXIS. 

The cerebro-spinal axis is formed from a superficial deposit of blastema, which 
occupies the whole width of the dorsal furrow, that elongated depression whose 
margins come together to complete the walls of the cranio-vertebral cavity (p. 15). 
This layer of blastema increases in 
thickness in each lateral half, while in Fig. 386. 

A. 

Fig. 386. PRIMITIVE FORM OF THE 
CEREBRO-SPINAL Axis IN THE EM- 
BRYO OF THE BIRD. Magnified. 

A and B (from Reichert) outlines of 
the dorsal aspect of the embryo bird at 
twenty-four and thirty-six hours of in- 
cubation. In A, the sides of the pri- 
mitive groove have united to a great 
extent and converted it into a canal, 
dilated at the cephalic extremity, 2 ; 
6, the cephalic fold of the germinal 
membrane ; 8, the primordial vertebral 
masses ; 9, the unclosed lumbar part 
of the vertebral groove. In B, 10, 11, 
and 12 indicate the partial division of the 
cephalic portion of the tube into the 
three primary vesicles ; 13, the rudi- 
ment of the eye ; 14, that of the ear. 

C, represents a transverse section of 
the body of the embryo previous to the 
closure of the vertebral groove. 1, 
chorda dorsalis; 2, primitive vertebral 
groove ; 2 to 3, medullary plates con- 
tinuous at 3, with 4, the corneous layer 
of the blastoderm ; 5, the ventral plates 
of the middle layer ; 6, the lowest or epi- 
thelial layer; 7, the primordial vertebral 




Fig. 387. 



Fig. 387. TRANSVERSE SECTION OF THE CERVICAL 
PART OF THE SPINAL CORD OF A HUMAN EMBRYO OF 
Six WEEKS (from Kolliker). * 

This and the following figure are only sketched, the 
white matter and a part of the grey not being shaded 
in. c, central canal ; e, its epithelial lining ; at e 
(inferiorly), the part which becomes the anterior com- 
missure ; at e' (superiorly) the part which becomes 
the posterior commissure ; a, the white substance of 
the anterior columns, beginning to be separated from 
the grey matter of the interior, and extending round 
into the lateral column, where it is crossed by the 
line from g, which points to the grey substance ; p t 
posterior column ; a, r, anterior roots ; p, r, posterior 
roots. 



the middle line the primitive groove it remains 
thin and depressed. The thin middle portion is 

that which forms in the spinal cord the anterior commissure. At the same time 
that the walls of the cranio-vertebral cavity are completed behind, the lateral margins 
of the cerebro-spinal axis are also bent backwards and meet together, so as to form 
a tube ; and this line of junction is the rudiment, in the spinal cord, of the posterior 
commissure, while the space within the cylinder is the central canal. The closure of 
the canal first takes place in the cervical region, and subsequently proceeds thence 
backwards in the dorsal, lumbar, and sacral regions. 




574 



DEVELOPMENT OF THE CEREBRO-SPINAL AXIS. 



The SPINAL CORD has been found by Kblliker already in the form of a cylinder in 
the cervical region of an embryo four weeks old. Ununited borders have been seen 
by Tiedemann in the ninth week towards the lower end of the cord, the perfect closing 
of the furrow being delayed in that part, which is slightly enlarged and presents a 
longitudinal median slit, analogous to the rhomboidal sinus in birds. 

The anterior fissure of the cord is developed very early, and contains even at first a 
process of the pia mater. 

The cervical and lumbar enlargements opposite the attachments of the brachial and 
crural nerves, appear at the end of the third month : in these situations the central 
canal, at that time not filled up, is somewhat larger than elsewhere. 



Fig. 388. 




Fig. 388. TRANSVERSE SECTION OF HALF 
THE CARTILAGINOUS VERTEBRAL COLUMN 
AND THE SPINAL CORD IN THE CERVICAL 
PART OF A HUMAN EMBRYO OF FROM 
NINE TO TEN WEEKS ^from Kolliker). J^ 

c, central canal lined with epithelium ; 
a, anterior column; p, posterior column; 
p', band of Goll ; g, ganglion of the 
posterior root ; p r, posterior root ; a r, 
anterior root passing over the ganglion ; 
dm, dura matral sheath, omitted near p r, 
to show the posterior roots ; b, body of 
the vertebra ; c h, chorda dorsalis ; n a, 
neural arch of the vertebra. 



At first the cord occupies the whole 
length of the vertebral canal, so that 
there is no cauda equina. In the fourth 
month the vertebrae begin to grow more 
rapidly than the cord, and the latter 
seems as it were to have retired up into 
the canal, and the elongation of the roots 
of the nerves which gives rise to the cauda 
equina is commenced. At the ninth 
month, the lower end of the cord is 
opposite the third lumbar vertebra. 

In textual composition the spinal cord consists at first, after the completion of its 
cylindrical form, entirely of uniform-looking cells. These separate into two layers, 
the inner of which forms the epithelium and surrounding connective tissue, or neu- 
roglia of the central canal, while the outer forms the grey substance of the cord. The 
white substance appears later than the grey, forming a layer external to it, and sepa- 
rated from an early period into an antero-lateral and a posterior column on each side. 
At a somewhat later period the white mass of these columns, increasing greatly in 
size, gives rise to the formation and gradually increasing depth of the anterior and 
posterior median fissures. At the same time, however, the lateral masses of grey 
substance also undergo extension in the parts named the cornua. It would appear 
that the integral nerve-fibres are at first developed from radiating processes which 
proceed from the cells of the grey substance. (Kolliker, Entwicklungsgeschichte ; 
Lockhart Clarke, in the Phil. Trans. 1862 ; Bidder und Kupfer, Untersuch. iib. d. 
Euckenmark, Leipz., 1857.) 

It may also be mentioned that, according to Remak and Kb'lliker, the roots of the 
spinal nerves and the ganglion are at first unconnected with the cord. The mass of 
blastema forming the ganglion first becomes apparent, and from this the posterior root 
seems to gro w towards, and later to become attached to, the cord ; while the anterior roots 
seem to extend outwards from the cord and to unite themselves later with the nerve. 
The central canal is at first nearly cylindrical ; it then becomes flattened at the 
sides, projecting deeply backwards and forwards. Between the eighth and tenth 
weeks it is greatly narrowed, and subsequently, being more and more confined to 
the centre, it ultimately diminishes to a small tube. The epithelial cells which line 
it from the first are long or columnar, and they retain this form in the adult. 



FORMATION OF THE EXCEPHALOX. 
THE EXCEPHALOX. 



575 



The brain is originally not to be distinguished from the spinal cord, being in fact 
the anterior portion of the medullary tube. It is soon altered in form, however, by 
the expansion of its walls in certain parts, while others enlarge in a less degree, and it 
then presents the appearance of a series of three cerebral vesicles, usually designated 
by embryologists the primary cerebral vesicles. 



Fig. 389. SKETCHES OF THE PRIMITIVE PARTS 
OF THE HUMAN BRAIN (from Kolliker). 



Fig. 389. 




1, 2, and 3 are from a human embryo of 
about seven weeks. 1, view of the whole 
embryo from behind, the brain and spinal cord 
exposed ; 2, the posterior, and 3, the lateral 
view of the brain removed from the body ; A, 
the anterior part of the first primary vesicle 
or cerebral hemisphere (prosencephalon) ; z, 
the posterior part of the same vesicle (dien- 
cephalon) ; i', the lower part of the same ; m, 
the middle primary vesicle (inesencephalon) ; e, 
the cerebellum or upper part of the third 
primary vesicle (epencephalon) ; m o, the lower 
part of the third primary vesicle or medulla 
oblongata. The figure 3 illustrates the several 
curves which take place in the development 
of the parts from the primitive medullary tube. In 4, a lateral vie* is given of the 
brain of a human embryo of three months : the enlargement of the cerebral hemisphere 
has covered in the optic thalami, leaving the tubercula quadrigemina, m, apparent. 

The changes which take place in the growth of the brain were first elaborately 
described by Tiedemann ; they have been investigated by Von Baer, Bischoff, Remak, 
Kolliker, and others, and have recently received additional elucidation from the 
researches of Reichert. (Tiedemann, " Anatomic und Bildungsgeschichte des 
Gehirns," Nuremberg, 1816 ; Reichert, " Bail des Menschlichen Gehirns," Leipzig. 
1861 ; F. Schmidt, " Beitrage z. Entwick. des Gehirns," in Zeitschr. f. Wissen. Zool. 
1862 ; Kolliker, Entwicklungsgeschichte, 1861.) 

DEVELOPMENT OP THE PRIMARY VESICLES. The anterior or first vesicle, is the part 
from which are developed the third ventricle, the optic thalami, the corpora striata, 
and the cerebral hemispheres. 

The middle or second vesicle, forms the corpora quadrigemina above, and the crura 
cerebri below, its cavity remaining as the Sylvian aqueduct. 

The posterior or third vesicle, continues incomplete above for some time, in so far as 
relates to its nervous substance. At length its anterior portion is closed over and forms 
the cerebellum above, whilst in its under part the pons Varolii is produced. The 
posterior portion, on the other hand, continues open on its dorsal aspect, and forms the 
medulla oblongata and fourth ventricle. 

Fig. 390. LONGITUDINAL SECTION OF THE 
CRANIAL CAVITY OF THE HUMAN EMBRYO AT 
FOUR WEEKS (from Kolliker). 

1, 2, 3, 4, and .*>, mark the depressions in 
the cranial wall which contain respectively the 
cerebral hemispheres, the thalarai, the corpora 
quadrigemina, the cerebellum, an,l the medulla 
oblongata; in 1, at o, the depression of the eye, 
and at o', the optic nerve is seen ; in 5, at a u, 
the primary auditory vesicle ; p, process from 
the phai'ynx, supposed by llathke to be con- 
nected with the formation of the pituitary 
body or hypophysis cerebri ; t, t, middle 
cranial septum or teutorium. 

These three vesicles, at first arranged in a straight line, one before the other, soon 




576 



DEVELOPMENT OF THE CEREBRO-SPINAL AXIS. 



alter their position, in correspondence with the curving downwards of the cephalic 
end of the embryo. Thus, at the seventh week there is an angular bend forwards 
between the hindmost vesicle and the rudimentary spinal cord, the projecting angle 
(backwards) being named the cervical tuberosity. Another bend, but in the opposite 
direction, exists between that part of the third vesicle which forms the medulla 
oblongata, and that which gives rise to the cerebellum. Lastly, a third angle is pro- 
duced by a bend forwards and downwards in the region of the middle vesicle, from 
which the corpora quadrigemina are developed, and which forms, at this period, the 
highest part of the encephalon ; whilst the anterior, or first vesicle, is bent nearly at a 
right angle downwards. 





Fig. 391. Fig. 391. SKETCHES OF THE EARLY 

FORM OF THE PARTS OF THE 

CEREBRO- SPINAL Axis IN THE 
HUMAN EMBRYO (after Tiede- 
mann). 

A, at the seventh week, lateral 
view ; 1, spinal cord ; 2, medulla 
oblongata ; 3, cerebellum ; 4, mid- 
dle vesicle or corpora quadrigemina; 
5, 6, 7, first vesicle. B, at the 
ninth week, posterior view ; 1, 
medulla oblongata ; 2, cerebellum ; 
3, corpora quadrigemina ; 4, 5, tha- 
lami optici and cerebral hemispheres. 
C and D, lateral and posterior views 
of the brain of the human embryo 
at twelve weeks, a, cerebrum ; b, 
corpora quadrigemina ; c, cere- 
bellum ; d, medulla oblongata ; the 
thalami are now covered by the 
enlarged hemispheres. E, posterior 
view of the same brain dissected to 
show the deeper parts. 1, medulla 
oblongata ; 2, cerebellum ; 3, cor- 
pora quadrigemina ; 4, thalami 
optici ; 5, the hemisphere turned 
aside ; 6, the corpus striatum em- 
bedded in the hemisphere ; 7, the 
commencement of the corpus cal- 
losum. F, the inner side of the 
right half of the same brain sepa- 
rated by a vertical median section, 
showing the central or ventricular 
cavity. 1, 2, the spinal cord and 
medulla oblongata, still hollow ; 3, 
bend at which the pons Varolii is 
formed ; 4, cerebellum ; 5, lamina 

(superior cerebellar peduncles) passing up to the corpora quadrigemina ; 6, crura cerebri ; 
7, corpora quadrigemina, still hollow ; 8, third ventricle ; 9, infundibulum ; 10, thata- 
mus, now solid ; 11, optic nerve ; 12, cleft leading into the lateral ventricle ; 13, com- 
mencing corpus callosum. 





F 





At an early period of the development of the brain, the anterior primary vesicle 
undergoes a peculiar change, by which two sets of parts are originated, the first of 
which corresponds to the cerebral hemispheres, the second to the thalami optici ; the 
middle vesicle, remaining single, gives rise to the corpora quadrigemina ; and the 
posterior vesicle, like the first, but at a somewhat later period, serves as the basis of 
the rudiments of two parts, viz., the cerebellum and the medulla oblongata. Thus, 
out of the three primary vesicles five fundamental parts of the encephalon are 
formed. 

The following tabular statement may serve as a synoptical view of the relation 



PARTS DERIVED FROM PRIMARY CEREBRAL VESICLES. 577 

subsisting between the primary encephalic vesicles, the five fundamental parts, and 
the principal permanent structures of the brain : 

( Cerebral Hemispheres, Corpus Callosum, 

/I. Prosencephalon. * I Corpora Striata, Fornix, Lateral Yen- 
I. Anterior primary Vesicle J ' tricles ' Olfa 'tory nerve. 

U Diencephalon. 

II. Middle primary Vesicle, 3. Mesencephalon. 

. ,-, , , ( Cerebellum, Pons Varolii, anterior part of 

f 4 - Epencephalon. J th(J Fom ^ Ventricle> 

III. Posterior primary Vesicle, < 

I , ,, . , . ( Medulla Oblongata, Fourth Ventricle, Au- 

lo. Metencephalon. { ditory nerve * 

At a later period of development, the anterior part of the first vesicle, which, as 
stated above, represents the cerebral hemispheres, increases greatly in size upwards 
and backwards, and gradually covers the parts situated behind it ; first the thalami, 
then the corpora quadrigemina, and lastly the cerebellum. 

On laying open the rudimentary encephalon, two tracts of nervous matter are seen 
to be prolonged upwards from the spinal cord upon the floor of the cephalic vesicles ; 
these tracts, which are doubtless connected with the anterior and lateral parts of the 
cord, are the rudiments of the crura cerebri and corresponding columns of the 
medulla oblongata. 

FARTHER DEVELOPMENT OF THE PRIMARY VESICLES. The third vesicle. The poste- 
rior portion of this vesicle, corresponding with the medulla oblongata, is never closed 
above by nervous matter. The open part of the medullary tube constitutes the'floor 
of. the fourth ventricle, which communicates below with the canal of the spinal cord, 
at the place where the calamus scriptorius is eventually formed. 

The three constituent parts of the medulla oblongata begin to be distinguished about 
the third month ; first the restiform bodies, which are connected with the commencing 
cerebellum, and afterwards the anterior pyramids and olives. The anterior pyramids 
become prominent on the surface and distinctly denned in the fifth month ; and by 
this time also their decussation is evident. The olivary fasciculi are early distin- 
guishable, but the proper olivary body, or tubercle, does not appear till about the 
sixth month. The fasciolae, cinerece of the fourth ventricle can be seen at the fourth 
or fifth month, but the white strice not until after birth. 

The anterior part of the third vesicle is soon closed above by nervous substance, 
and forms the commencing cerebellum. This part exists about the end of the second 
month, as a delicate medullary lamina, forming an arch behind the corpora quadri- 
gemina across the widely open primitive medullary tube. 

According to Bischoff, the cerebellum does not commence, as was previously sup- 
posed, by two lateral plates which grow up and meet each other in the middle line ; but 
a continuous deposit of nervous substance takes place across this part of the medullary 
tube, and closes it in at once. This layer of nervous matter, which is soon connected 
with the corpora restiformia, or inferior peduncles, increases gradually up to the fourth 
month, at which time there may be seen on its under surface the commencing corpus 
dentatum. In the fifth month a division into five lobes has taken place ; at the sixth, 
these lobes send out folia, which are at first simple, but afterwards become subdivided. 
Moreover, the hemispheres of the cerebellum are now relatively larger than its 
median portion, or worm. In the seventh month the organ is more complete, 
and the flocculus and posterior velum, with the other parts of the inferior vermiform 
process, are now distinguishable, except the amygdala, which are later in their 
appearance. 

Of the peduncles of the cerebellum, the inferior pair (corpora restiformia) are the 
first seen viz., about the third month ; the middle peduncles are perceptible in the 
fourth month ; and at the fifth, the superior peduncles and the Vieussenian valve. 

* This and the four following terms are adopted as applicable to the principal secondary 
divisions of the primordial medullary tube, and as corresponding to the commonly received 
names of the German embryologists, viz., Vorderhirn, Zwischenhirn, Mittelhirn, Hinter- 
hirn, and Nachhirn ; or their less used English translations, viz., forebrain, interbrain, 
midbrain, hindbrain, and afterbrain. 



578 



DEVELOPMENT OF THE CEREBRO-SPINAL AXIS. 



The pons Varolii is formed, as it were, by the fibres from the hemispheres of the 
cerebellum embracing the pyramidal and olivary fasciculi of the medulla oblongata. 
According to Baer, the bend which takes place at this part of the encephalon 
thrusts down a mass of nervous substance before any fibres can be seen ; and in 
this substance transverse fibres, continuous with those of the cerebellum, are after- 
wards developed. From its relation to the cerebellar hemispheres the pon.s keeps 
pace with them in its growth ; and, in conformity with this relation, its transverse 
fibres are few, or entirely wanting, in those animals in which there is a corresponding 
deficiency or absence of the lateral parts of the cerebellum. 

Fig. 392. Fig. 392 A. BRAIN AND SPINAL CORD EXPOSED FROM BEHIND IN 

^ A FOSTUS OF THREE MONTHS (from Kolliker). 

h, the hemispheres ; m, the mesencephalic vesicle or corpora 
quadrigemina ; c, the cerebellum ; below this are the medulla 
oblongata, mo, and fourth ventricle, with remains of the membrana 
obturatoria. The spinal cord, s, extends to the lower end of the 
sacral canal and presents the brachial and crural enlargements. 

Fig. 392 B. UPPER VIEW OF THE BRAIN OF A THREE MONTHS' 

FffiTUS, IN WHICH THE HEMISPHERES HAVE BEEN DIVIDED AND 
TURNED ASIDE, AND THE VESICLE OF THE MESENCEPHALON (CoR- 

PORA QDABRIGEMINA) OPENED (from Kolliker). 

/, anterior part of the great arch of the hemispheres over the 
cerebral fissure ; f, posterior part descending into the cornu am- 
monis ; cs, corpus striatum ; th, thalaraus opticus ; m, in the 
floor of the opened vesicle of the mesencephalon, which is still 
hollow. 

The second, or middle vesicle. The corpora quadrigemina 
are formed in the upper part of the middle cephalic vesicle ; 
the hollow in the interior of which communicates with those 
of the first and third vesicles. The corpora quadrigemina, in 
the early condition of the human embryo, are of great propor- 
tionate volume, in harmony with what is seen in the lower 
vertebrata : but subsequently they do not grow so fast as the 
anterior parts of the encephalon, and are therefore soon 
overlaid by the cerebral hemispheres, which at the sixth month 
cover them in completely. Moreover, they become gradually 
solid by the deposition of matter within them ; and as, in the 
meantime, the cerebral peduncles are increasing rapidly in size 
in the floor of this middle cephalic vesicle, the cavity in its 
interior is quickly filled up, with the exception of the narrow 
passage named the Sylvian aqueduct. The fillet is distinguish- 
able in the fourth month. The corpora quadrigemina of the 
two sides are not marked off from each other by a vertical 
median groove until about the sixth month ; and the trans- 
verse depression separating the anterior and posterior pairs' 
is first seen about the seventh month of intra-uterine life. 

The first, or anterior vesicle. This vesicle, very soon after its formation, exhibits 
two lateral outgrowths the optic vesicles, destined to form the fundamental parts of 
the organs of vision. Each of these soon becomes separated from the parent vesicle 
by a constricted part, which forms the optic nerve and tract. The first vesicle has 
usually been described as dividing into two portions viz., a posterior, which is 
developed into the optic thalami and third ventricle, and an anterior, which forms the 
principal mass of the cerebral hemispheres, including the corpora striata. Reichert, 
however, has pointed out that the hemispheres and corpora striata are developed 
from the sides of the fore part of the vesicle, and become distinguished from it by a 
constriction similarly as the optic vesicles had previously been, and that there is left 
between the hemisphere-vesicles of opposite sides a wedge-shaped interval, which forms 
the third ventricle. He points out that the terminal extremity of the cerebro-spinal 
tube is at the tip of this wedge, and is placed immediately in front of the optic 
commissure, at the lamina cinerea ; and that therefore the infundibulum is not that 





PINEAL GLAND. OPTIC TEAL AMI. 



579 



Fig. 393. 



extremity, as had been previously supposed by Baer, but is an expansion of the vesicle 
downwards, in similar fashion as there is an expansion of it upwards in the region of 
the pineal body. 

The pituitary body was asserted by Rathke to be derived 
from a prolongation upwards of the mucous membrane of the 
pharynx into the base of the skull between the trabeculse. It 
appears, however, from the researches of Reichert and Bidder, 
that the base of the skull is never imperfect in this region. 
Reichert suggested that the pituitary body might be derived 
from the extremity of the chorda dorsalis, but is now rather 
inclined to think that it is a development of the pia mater. 

Fig. 393. BRAIN AND SPINAL CORD OP A FOSTUS OF POUR 

MONTHS, SEEN FROM BEHIND (from Kolliker). 

k, hemispheres of the cerebrum ; m, corpora quadrigemina 
or mesencephalon ; c, cerebellum ; m o, medulla oblongata, the 
fourth ventricle being overlapped by the cerebellum j s, s, the 
spiual cord with its brachial and crural enlargements. 

The pineal gland, according to Baer, is developed from 
the back part of the thalami, where those bodies continue 
joined together ; but it is suggested by Bischoff that its 
development may be rather connected with the pia mater. 
It was not seen by Tiedemann until the fourth month ; sub- 
sequently its growth is very slow ; and it at first contains no 
gritty deposit : this, however, was found by Sb'mmerring at 
birth. 

The two optic thalami, formed from the posterior part of 
the anterior vesicle, consist at first of a single hollow sac of 
nervous matter, the cavity of which communicates in front 
with the interior of the commencing cerebral hemispheres, and 
behind with that of the middle cephalic vesicle (corpora 
quadrigemina). Soon, however, by means of a deposit taking place in their interior 

Fig. 394. 





Fig. 394. SEMIDIAGRAMMATIC VIEWS OP THE INNER SURFACE OP THE RIGHT CEREBRAL 
HEMISPHERE OP THE FCETAL BKAIN AT VARIOUS STAGES OP DEVELOPMENT (from 
Schmidt). 

1, 2, and 3, are from foetuses of the respective ages of eight, ten, and sixteen weeks ; 
4, from a foetus of six months, a, lamina terminalis or part of the first primary vesicle 
which adheres to the sella turcica ; 6, section of the cerebral peduncle as it passes into 
the thalamus and corpus striatum ; the arched line which surrounds this bounds the great 
cerebral fissure ; c, anterior part of the fornix and the septum lucidum ; d, inner part 
of the arch of the cerebrum, afterwards the hippocampus major and posterior part of the 
fornix ; e, corpus callosum, very short in 3, elongated backwards in 4 ; in 4, /, the 
superior marginal convolution; /', fronto-parietal fissure ; g, gyrus fornicatus ; p', the 
internal vertical fissure descending to meet the fissure of the hippocampus ; I, olfactory 
bulb ; F, P, 0, T, frontal, parietal, occipital and temporal lobes. 



580 DEVELOPMENT OF THE CEREBRO-SPINAL AXIS. 

behind, below, and at the sides, the thalami become solid, and at the same time a 
cleft or fissure appears between them above, and penetrates down to the internal 
cavity, which continues open at the back part opposite the entrance of the 
Sylvian aqueduct. This cleft or fissure is the third ventricle. Behind, the two 
thalami continue united by the posterior commissure, which is distinguishable 
about the end of the third month, and also by the peduncles of the pineal gland. The 
soft commissure could not be detected by Tiedemann until the ninth month ; but its 
apparent absence at earlier dates may perhaps be attributed to the effects of laceration. 

At an early period the optic tracts may be recognised as hollow prolongations from 
the outer part of the wall of the thalami while they are still vesicular. At the fourth 
month these tracts are distinctly formed. 

The hemisphere-vesicle becomes divisible into two parts : one of these is the part 
which from the interior appears as the corpus striatum, and from the exterior as the 
island of Reil, or central lobe; the other forms the expanded or covering portion 
of the hemisphere, and is designated by Reichert the mantle. The aperture existing 
at the constricted neck of the hemisphere vesicle, Schmidt and Reichert have recognised 
as the foramen of Monro. 

The corpora striata, it will be observed, have a very different origin from the optic 
thalami ; for, while the optic thalami are formed by thickening of the circumferential 
wall of a part of the first cerebral vesicle, and thus correspond in their origin 
with all the parts of the encephalon behind them, which are likewise derived from 
portions of the cerebro-spinal tube, the corpora striata appear as thickenings of the 
floor of the hemisphere-vesicles, which are lateral offshoots from the original cerebro- 
spinal tube. On this account, Reichert considers the brain primarily divisible into the 
stem, which comprises the whole encephalon forwards to the tsenia semicircularis, and 
the hemisphere-vesicles, which include the corpora striata and hemispheres. 

The cerebral hemispheres enlarging, and having their walls increased in thickness 
form, during the fourth month (Tiedemann), two smooth shell-like lamellee, which 
include the cavities afterwards named the lateral ventricles, and the parts contained 
within them. Following out the subsequent changes affecting the exterior of the 
cerebral hemispheres, it is found that about the fourth month the first traces of some 
of the convolutions appear, the intermediate sulci commencing only as very slight 




Fig. 395. THE SURFACE OF THE F<ETAL BRAIN AT Six MONTHS (from R. Wagner). 

This figure is intended to show the commencement of the formation of the principal 
fissures and convolutions. A, from above ; B, from the left side. F, frontal lobe ; P, 
parietal ; 0, occipital ; T, temporal ; a, a, a, slight appearance of the several frontal 
convolutions ; s, the Sylvian fissure ; s', its anterior division ; within it, C, the central 
lobe or convolutions of the island ; r } fissure of Rolando ; p, the vertical fissure (external 
part) ; t } the parallel fissure. 

depressions on the hitherto smooth surface. Though the hemispheres continue to 
grow quickly upwards and backwards, the convolutions at first become distinct by 



HEMISPHERES. CORPUS CALLOSUM. 



581 



comparatively slow degrees ; but towards the seventh and eighth months they are 
developed with great rapidity, and, at the beginning of the last month of intra-uterine 
life, all the principal ones are marked out. 

The S'/lvian fissure, which afterwards separates the anterior from the middle lobe 
of each hemisphere, begins as a depression or cleft between them about the fourth 
month, and, after the gre-it longitudinal, is the first of the fissures to make its 
appearance. It is followed by the fissure of Rolando, and the vertical fissure, and 
somewhat later by the internal fronto -parietal fissure. After this, the various sub- 
ordinate fissures dividing the convolutions gradually make their appearance. By the 
end of the third month the hemispheres have extended so far backwards as to cover 
the thalami ; at the fourth they reach the corpora quadrigemina ; at the sixth they 
cover those bodies and great part of the cerebellum, beyond which they project still 
further backwards by the end of the seventh month. 

During the growth of the hemisphere the aperture of the foramen of Monro is 
extended backwards ; the arched margin of this opening is curved downwards at 
its extremities, and forms anteriorly the fornix, and posteriorly the corpus fimbriatum 
and hippocampus major ; above the margin a part of the wall of each hemisphere 
comes into contact with its fellow, and in the lower part forms the septum lucidum, 
while above this the hemispheres are united by the development of the great 
commissure, the corpus callosum. 

The corpus callosum is described by Tiedemann as being first seen about the end of 
the third month, as a narrow vertical band, extending across between the forepart of 
the two hemispheres, and subsequently growing backwards. With this view the 
observations of Schmidt coincide. Reichert, however, maintains that the commissural 
structure seen at the forepart of the hemispheres is the anterior white commissure, 
and that the corpus callosum appears in its whole extent at once. 

The corpora albicantia at first form a single mass : so also do the anterior pillars 
of the fornix, which are distinguished before the posterior pillars. The posterior 
pillars are not seen until the fourth or fifth month. At that period the hippocampus 
minor is also discernible. 

Fig. 396. VIEW OP THE INNER Fig. 396. 

SURFACE OF THE RIGHT HALF 
OF THE FCETAL BRAIN OF ABOUT 
six MONTHS (from Reichert). 

F, frontal lobe; P, parietal; 
0, occipital; T, temporal; I, 
olfactory bulb ; II, right optic 
nerve ; fp, fronto-parietal fissure ; 
p, vertical fissure ; />', inter- 
nal vertical fissure ; Ti, hippo- 
campal fissure ; g, gyrus forni- 
catus ; c, c, corpus callosum ; 
s, septum lucidum ; f, placed 
between the middle commissure 
and the foramen of Monro ; 
v, in the upper part of the 
third ventricle immediately below 
the velum interpositum and for- 
nix : v', in the back part of the 

third ventricle below the pineal gland, and pointing by a line to the aqueduct of Sylvius ; 
v", in the lower part of the third ventricle above the infundibulum ; r, recessus pinealis 
passing backwards from the tela choroidea; p v, pons Varolii; Ce, cerebellum. 

MEMBRANES OF THE ENCEPHALON. 

It is remarked by Bischoff, that the pia mater and arachnoid are formed by the 
separation of the outer layer of the primitive cephalic mass ; and thus that the pia 
mater does not send inwards processes into the fissures or sulci, nor into the ventri- 
cular cavities ; but that every part of this vascular membrane, including the choroid 
plexuses and velum interpositum, is formed in its proper position in connection 
Avith the nervous matter. The dura mater, on the other hand, is developed from the 
inner surface of the dorsal plates. 




582 



THE CRANIAL NERVES. 



The pia mater and dura mater have both been detected about the seventh or 
eighth week, at which period the tentorium cerebelli exists. At the third month 
the falx cerebri, with the longitudinal and lateral sinuses, are perceptible; and the 
choroid plexuses of both the lateral and fourth ventricles are distinguishable. No 
trace of arachnoid, however, can be seen until the fifth month. 

II. THE CEREBRO-SPINAL NERVES. 

The nerves directly connected with the great cerebro-spinal centre 
constitute a series of symmetrical pairs, the number of which has been 
variously estimated from forty to forty- three. Of these nerves, when esti- 
mated at the smaller number, nine issue from the cranium through different 
foramina or apertures in its base, and are thence strictly named cranial. 
The teuth nerve passes out between the occipital bone and the first vertebra, 
and the remaining thirty nerves all issue below the corresponding vertebral 
pieces of the spine. To the whole series of thirty-one nerves the name of 
spinal is usually given. 

A. CRANIAL NERVES. 

The cranial nerve?, besides being named numerically, according to the 
relative position of the apertures for their exit from the cranium, have 
likewise been distinguished by other names, according to the place or 
mode of their distribution, and according to their functions or other circum- 
stances. 

The number of the cranial nerves has been variously stated as nine or as 
twelve by different anatomists ; the difference consisting mainly in this, 
that, under one system, the nerves which enter the internal auditory 
meatus, and those which pass through the jugular foramen, are in each 
case considered a single pair (seventh and eighth) divisible into parts ; 
while under another system each of the nerves is held to constitute a 
distinct pair. The following table presents a synoptical view of the cranial 
nerves under these two modes of enumeration, as in the respective systems 
of Willis and of Sommerring. 



Olfactory nerves. 

Optic. 

Oculo-motor. 

Pathetic or trochlear. 

Trifacial or trigeminal. 

Abducent ocular. 

Facial motor. 

Auditory. 

Glosso-pharyngeal. 

Pneumo-gastric. 

Spinal accessory. 

Hypoglossal or lingual motor. 

The arrangement of Sommerring is the preferable one, as being the 
simplest and most natural ; for each of the parts included in the seventh 
and eighth pairs of Willis is really a distinct nerve. But as the plan of 
Willis is still in more general use, it will most conveniently be followed 
here. The cranial nerves will therefore, when not otherwise designated, be 
referred to as consisting of nine pairs. 

* Willis described the glosso-pharyngeal nerve as a branch of the vagus, and included 
the suboccipital nerve as a tenth among the cranial nerves. 



WILLIS* 


SCEMMERIUNQ. 


First pair of nerves 


First pair of nerves 


Second 


Second 


} , 


Third 


Third 


1 


Fourth 


Fourth 


> 


Fifth 


Fifth 




Sixth 


Sixth 


i 


( nervusdurus 


Seventh 


1 


Seventh w | n< mollis . 


Eighth 


> . 


in. vagus 


( Ninth 


, . 




\ Tenth 


t . 


accessorius. 


Eleventh 


, . 


Ninth 


Twelfth 


> 



ORIGIN OF THE "CRANIAL NERVES. 



83 



CONNECTIONS OF THE CRANIAL NERVES WITH THE ENCEPHALON. 

The roots of the cranial nerves may be traced for some depth into the 
substance of the encephalon, a circumstance which has led to the distinction 
of the deep or real origin, and the superficial or apparent origin, by which 
latter is understood the place at which the nerve appears to be attached to 
the surface of the encephalon. The superficial origin of these nerves is 
quite obvious, but their deeper connection is, in most cases, still a matter 
of some uncertainty. 



Fig. 397. VIEW FROM 

BELOW OF THE CONNEC- 
TION OF THE PRINCIPAL 
NERVES WITH THE 
BRAIN. 

The full description of 
this figure will be found 
at p. 538. The following 
references apply to the 
roots of the nerves : I', 
the right olfactory tract 
divided near its middle ; 
II, the left optic nerve 
springing from the com- 
missure which is con- 
cealed by the pituitary 
body ; II', the right optic 
tract; the left tract is 
seen passing back into 
i and e, the internal and 
external corpora genicu- 
lata ; III, the left oculo- 
motor nerve ; IV, the 
trochlear ; V, V, the 
large roots of the tri- 
facial nerves ; + + , the 
lesser roots, the -r of the 
right side is placed on 
the Grasserian ganglion ; 
1, the ophthalmic ; 2, the 
superior maxillary, and 
3, the inferior maxillary 
nerves ; VI, the left ab- 
ducent nerve ; VII, a, &, 
the facial and auditory 
nerves ; a, VIII, 6, the 
glosso-pharyngeal, pneu- 
mo -gastric, and spinal ac- 
cessory nerves ; IX, the 
right hypoglossal nerve ; 
at o, on the left side, the 
rootlets are seen cut- 
short ; C I, the left sub- 
occipital or first cervical 
nerve. 



Fig. 397. 




Ci 



cL ca 



1. The first or olfactory nerve, as it is usually described, small in man in 
comparison with animals, lies on the under surface of the anterior lobe of the 
cerebrum to the outer side of the longitudinal median fissure, lodged in a 
sulcus between two straight convolutions. Unlike other nerves, it consists 
of a large proportion of grey matter mixed with white fibres, and indeed 



584 THE CRANIAL NERVES. 

agrees closely in structure with the cerebral substance. It swells into an oval 
enlargement, the olfactory bulb, in front, which also contains much grey 
matter, and from this part small soft nerves descend through the cribriform 
plate into the nose. When traced backwards, it is found to be spread out 
and attached behind to the under surface of the anterior lobe by means of 
three roots, named external, middle, and internal, which pass in different 
directions. The bulbous part is therefore rather to be regarded as an 
olfactory lobe of the cerebrum than as a part of a true nerve, while the 
white part prolonged backwards into the brain, together with its so-called 
roots, may be termed the olfactory tract. 

The external or long root consists of a band of medullary fibres, which 
passes, in the form of a white streak, outwards and backwards along the 
anterior margin of the perforated space, towards the posterior border of the 
Sylvian fissure, where it may be followed into the substance of the cere- 
brum. Its further connections are doubtful, but it has been stated that its 
fibres have been traced to the following parts, viz., the convolutions of the 
island of Reil, the anterior commissure, and the superficial layer of the 
optic thalamus (Valentin). 

The middle or grey root is of a pyramidal shape, and consists of grey 
matter on the surface, which is prolonged from the adjacent part of the 
anterior lobe and perforated space. Within it there are white fibres, which 
have been traced to the corpus striatum. 

The internal root (short root, Scarpa), which cannot always be demon- 
strated, is composed of white fibres which may be traced from the inner and 
posterior part of the anterior lobe, where they are said by Foville to be 
connected with the longitudinal fibres of the gyrus fornicatus. 

The question whether the olfactory bulbs ought to be considered as nerves or as 
cerebral lobes is, if tested by reference to the history of development, not so simple 
as might at first appear. It is in favour of their being regarded as lobes, that in 
the lower vertebrate animals the olfactory bulbs are generally recognised by com- 
parative anatomists as additional encephalic lobes, and that in most mammals they 
are much larger proportionally than in man, and frequently contain a cavity or 
ventricle in their interior, and further that in their minute structure they nearly 
agree with the cerebrum ; but, as it is known that in the first development of the 
eye the peripheral part or retina, as well as the rest of the optic nerve, is originally 
formed by the extension of a hollow vesicle from the first foetal encephalic compart- 
ment, so in the case of the olfactory nerve, although the peripheral or distributed part 
is of separate origin from the olfactory bulb, the latter part is comparable in its 
origin with the optic vesicle. 

2. The second pair or optic nerves of the two sides meet each other at 
the optic commissure (chiasma), where they partially decussate. From this 
point they may be traced backwards round the crura cerebri, under the 
name of the optic tracts. 

Each optic tract aiises from the optic thalamus, the corpora quadri- 
gemina, and the corpora geniculata. As it leaves the under part of the 
thalamus, it makes a sudden bend forwards and then runs obliquely across 
the under surface of the cerebral peduncle, in the form of a flattened band, 
which is attached by its anterior surface to the peduncle ; after this, becoming 
more nearly cylindrical, it adheres to the tuber cinereum, from which and, as 
stated by Yicq-d'Azyr, from the lamina cinerea it is said to receive an 
accession of fibres, and thus reaches the optic commissure. 

In the commissure the nerve-fibres of the two sides undergo a partial de- 
cussation. The outer fibres of each tract continue onwards to the eye of the 



ROOTS OF THE CEAXIAL NERVES. OPTIC. 



585 



same side : the inner fibres cross over to the opposite side ; and fibres have 
been described as running from one optic tract to the other along the 
posterior part of the commissure, while others pass between the two optic 
nerves in its anterior part (Mayo). 

In front of the commissure, the nerve enters the foramen opticum, 
receiving a sheath from the dura mater and acquiring greater firmness. 

Fig. 398. 




Fig. 398. LATERAL VIEW OF THE CONNECTION OP THE PRINCIPAL NERVES WITH THE 

BRAIN. 

The full description of this figure will be found at p. 553. The following references 
apply to the roots of the nerves ; I, the right olfactory tract cut near its middle ; II, the 
optic nerves immediately in front of the commissure ; the right optic tract is seen passing 
back to the thalamus (Th\ corpora geniculata (i, e,), and corpora quadrigemina (5) ; III, 
the right oculo-motor nerve ; IV, the trochlear nerve rising at v, from near the valve of 
Vieussens ; V, the trifacial nerve ; VI, the abducent ocular ; a, VII, &, the facial and 
auditory nerves, and between them the pars intermedia ; a, VIII, b, the roots of the 
glosso-pharyngeal, pneu mo-gastric, and spinal accessory nerves ; IX, the hypoglossal 
nerve ; C I, the separate anterior and posterior roots of the suboccipital or first cervical 



The fibres of origin of the optic tract from the thalamus are derived partly from the 
superficial stratum and partly from the interior of that body. According to Foville, 
this tract is also connected with the tsenia semicircularis, and with the termination 
of the gyrus fornicatus ; and he states further, that where the optic tract turns round 
the back of the thalamus and the cerebral peduncle it receives other delicate fibres, 
which descend from the grey matter of those parts. (Op. cit. p. 514.) 

Q Q 



586 THE CRANIAL NERVES. 

3. The third pair of nerves (motores oculorum) have their apparent or 
superficial origin from the inner surface of the crura cerebri in the inter- 
peduncular space, immediately in front of the pons. Each nerve consists 
of a number of funiculi which arise in an oblique line from the surface. 

The deeper fibres of origin, when followed into the cms, are found to diverge 
in its substance, some being traced to the locus niger, others running down- 
wards in the pons among its longitudinal fibres, and others turning upwards to be 
connected with the corpora quadrigemina and Vieussenian valve. According to 
Stilling, with whom Kolliker agrees, the major part of the fibres arise from a grey 
nucleus in the floor of the Sylvian aqueduct, close to the origin of some fibres of the 
fourth nerve. 

4. The fourth pair, pathetic or trochlear nerves, the smallest of those 
which are derived from the brain, are seen at the outer side of the crura 
cerebri immediately before the pons. Each nerve may be traced backwards 
round the peduncle to a place below the corpora quadrigemina, where it arises 
from the upper part of the valve of Vieussens. Kolliker states that, under 
the corpora quadrigemina, the fibres of origin are divided into two bundles ; 
the anterior being traceable through the lateral wall of the aqueduct of 
Sylvius to its floor, where it arises from a grey nucleus close to the middle 
line ; the posterior bundle being derived from a grey nucleus in the floor of 
the fourth ventricle, close to the origin of the fifth nerve. The roots of the 
nerves of opposite sides are connected together across the middle line in the 
form of a white band or commissure in the substance of the velum. 

5. The fifth pair of nerves, par trigeminum, trifacial nerves, take their 
superficial origin from the side of the pons Varolii, where the transverse 
fibres of the latter are prolonged into the middle crus cerebelli, considerably 
nearer to the upper than to the lower border of the pons. 

The fifth nerve consists of a larger or sensory, and a smaller or motor 
root. The smaller root is at first concealed by the larger, and is placed a 
little higher up, there being often two or three cross fibres of the pons 
between them. On separating the two roots, the lesser one is seen to 
consist of a very few funiculi. In the larger root the funiculi are numerous, 
amounting sometimes to nearly a hundred. 

Deep origin. The greater root runs behind the transverse fibres of the pons towards 
the lateral part of the medulla oblongata at the back of the olivary body. Several 
anatomists trace it into the floor of the fourth ventricle, between the fasciculi teretes 
and the restiform bodies. By some it is considered to be continuous with the fasci- 
culi teretes and lateral columns of the cord, whilst others connect it with the grey 
mass which is regarded by Stilling as the nucleus of the glosso-pharyngeal nerve. 

The motor root was supposed by Bell to descend to the pyramidal body, and 
Retzius believes that he has confirmed that opinion by dissection : but it would 
appear that the deep connection of this root is not yet known with certainty. 
According to Stilling the fibres pass through the pons to the floor of the fourth 
ventricle, and have their origin in its grey matter. 

According to Foville, some of the fibres of the sensory root of the fifth nerve are 
connected with transverse fibres in the pons, whilst others spread out on the surface 
of the middle peduncle of the cerebellum, and enter that part of the encephalon 
beneath the folia. (Op. cit. p. 506.) 

6. The sixth nerve (abducens), motor oculi externus, takes its apparent 
origin from between the pyramidal body and the pons Varolii by means 
of a larger and a smaller bundle. It is connected with the pyramid, and to 
a small extent with the pons also. Philipeaux and Vulpian, with whom 



ROOTS OF THE CRANIAL NERVES. 687 

Kolliker concurs, state that the fibres may be traced more deeply to the 
floor of the fourth ventricle. 

7. The seventh pair of nerves appear on each side at the posterior margin 
of the pons, between the middle and inferior peduncles of the cerebellum, 
and nearly in a line with the place of attachment of the fifth nerve. 

Deep origins. The portio dura or facial nerve, placed a little nearer to the middle 
line than the portio mollis, may be traced to the medulla oblongata between the resti- 
form and olivary fasciculi, with both of which it is said to be connected. Some of its 
fibres are derived from the pons. Philipeaux and Vulpian affirm that the fibres arise 
from the outer wall of the fourth ventricle, and that many of them decussate in its 
floor. 

Connected with the portio dura, and intermediate between it and the portio 
mollis, is a smaller white funiculus, first described by Wrisberg (portio inter duram et 
mollein). The roots of this accessory or intermediate portion are connected deeply 
with the lateral column of the cord. 

The portio mollis, or auditory nerve, rises from the floor of the fourth ventricle, at 
the back of the medulla oblongata, in which situation, as already described, trans- 
verse white striae are seen, which form the commencement of the nerve. These 
roots are connected with the grey matter, and some appear to come out of the median 
fissure. The nerve then turns round the restiform body, and becomes applied to the 
lower border of the pons, receiving accessions from the former of those parts, and 
according to some authors from the latter also. 

Eoville says that the roots of the portio mollis are also connected by a thin layer 
on the under surface of the middle peduncle with the cortical substance of the cere- 
bellum ; also, with the small lobule named the flocculus ; and with the grey matter at 
the borders of the calamus scriptorius. 

8. The eighth nerve consists of three distinct portions. 

The uppermost portion is the glosso-pharyngeal nerve ; next to this, and 
lower down, is the par vagum or pneumo-gastric nerve consisting of a larger 
number of cords. The roots of both these nerves are attached superficially 
to the fore part of the restiform. body. Still lower, is the spinal accessory 
nerve, which, ascending from the side of the spinal cord, enters the skull by 
the foramen magnum, and is associated with the pneumo-gastric nerve as it 
passes out through the foramen lacerum. 

The accessory nerve arises within the spinal canal from the lateral 
column of the cord behind its middle, by a series of slender roots, which 
commence as low down as the fifth or sixth cervical nerve. The nerve 
passes upwards between the posterior roots of the cervical nerves and the 
ligamentum deiiticulatuin, the several funiculi of origin successively joining 
it as it ascends. On entering the skull, it receives funiculi from the side 
of the medulla oblongata. 

These three portions of the eighth pair are connected deeply with grey nuclei 
within the cord and medulla oblongata, as already described (see p. 521 ). 

9. The ninth nerve (hypoglossal) arises, in a line continuous with that 
of the anterior roots of the spinal nerves, by scattered funiculi from the 
furrow between the olivary body and the anterior pyramid. 

The roots of the ninth nerve are traced by Stilling to one of the grey nuclei already 
described in the medulla oblongata, and they are said by Kolliker to undergo partial 
decussation in the floor of the fourth ventricle. 

DISTRIBUTION OF THE CRANIAL NERVES. 

Mode of exit from the cranium. Each of the cranial nerves issues at 
first from the cranial cavity through a foramen or tubular prolongation of 
the dura mater : some of these nerves or their main divisions are contained 

Q Q 2 



588 THE CRANIAL NERVES. 

in distinct foramina of the cranium, others are grouped together in one 
foramen. The numerous small olfactory nerves descend into the nose 
through the cribriform plate of the ethmoid bone ; the optic nerve pierces 
the root of the lesser wing of the sphenoid bone ; the third, fourth, and 
sixth nerves, with the ophthalmic division of the fifth nerve, pass through the 

Fig. 399. 




Fig. 399. INTERNAL VIEW OF THE B/SE OF THE SKULL, SHOWING THE PLACES OF EXIT OF 
THE CKANIAL NERVES. 

The dura mater is left in great part within the base of the skull ; the tentoriuin is 
removed and the venous sinuses are opened. Ou the left side a small portion of the roof 
of the orbit has been removed to show the relation of certain nerves at the cavernous 
sinus and in the sphenoidal fissure. The roots of the several cranial nerves have been 
divided at a short distance inside the foramina of the dura mater through which they 
respectively pass. I, the bulb of the olfactory nerve lying over the cribriform plate of 
the ethmoid bone ; II, the optic nerves, that of the left side cut short ; III, placed on the 
pituitary body, indicates the common oculo-motor nerve ; IV, the trochlear nerve ; V, is 
placed on the left side opposite to the middle of the three divisions of the trigeminus, 
which, together with the ganglion and greater root, have been exposed by opening up 
the dura mater ; on the right side the greater root is seen ; VI, placed below the foramen 
of exit of the abducent ocular ; VII, placed on the upper part of the petrous bone oppo- 
site the entrance of the facial and auditory nerves into the meatus auditorius internus ; 
VIII, placed on the petrous bone outside the jugular foramen opposite the place of exit 
of the three divisions of the eighth pair of nerves ; IX, placed upon the basilar part of 
the occipital bone in front of the hypoglossal nerve as it passes through the anterior 
condyloid foramen. On the left side at the cavernous sinus, the third, fourth, and 
ophthalmic division of the fifth nerves are seen keeping towards the outer side, while the 
sixth nerve is deeper and close to the internal carotid artery. The explanation of the 
remaining references in this figure will be found at p. 461. 



GENERAL DISTRIBUTION. 589 

sphenoidal fissure ; the superior maxillary and inferior maxillary divisions 
of the fifth pass respectively through the foramen rotundum and foramen 
ovale of the great wing ; the facial and auditory nerves pierce the petrous 
bone ; the three parts of the eighth pair descend in separate canals of the 
dura mater through the anterior part of the jugular foramen between the 
petrous and occipital bones ; and the hypoglossal nerve passes through the 
anterior condyloid foramen of the occipital bone. 

General distribution. The greater number of the cranial nerves are en- 
tirely confined in their distribution within the limits of the head ; as in the 
case of the first six pairs and the auditory nerve. Of these, the olfactory, 
optic, and auditory are restricted to their respective organs of sense ; while 
the third, fourth, and sixth are exclusively motor nerves in connection with 
the external and internal muscles of the eyeball and that of the upper eye- 
lid. In the remaining nerve, the fifth or trifacial, all the fibres derived 
from the greater root, and connected with the Gasseriau ganglion, are en- 
tirely sensory in their function, and constitute the whole of the first and 
second and the greater part of the third division of the nerve : but the 
last of these divisions has associated with it the fibres of the lesser root, 
so as to become in some degree a compound nerve. As a nerve of sensa- 
tion the trifacial occupies in its distribution the greater part of the head 
superficially and deeply, excepting the interior of the cranium and that 
part of the scalp which is situated in the region behind a perpendicular line 
passing through the external auditory meatus. The muscular distribution 
of the inferior division of the fifth nerve is chiefly to the muscles of masti- 
cation. 

Of the remaining nerves, the facial and hypoglossal, both exclusively 
motor in function, are almost entirely cephalic in their distribution ; the 
facial nerve giving fibres to all the superficial and a few of the deeper 
muscles of the head and face ; and the ninth or hypoglossal supplying the 
muscles of the tongue. Of the facial, however, a small branch joins 
one of the cervical nerves in the platysma myoides ; and of the ninth, the 
descending branch supplies in part the muscles of the neck which depress 
the hyoid bone and larynx. 

Of the three parts of the eighth pair, ranked as cranial nerves in conse- 
quence of their passing through one of the foramina of the cranium, two have 
only a very limited distribution in the head, and furnish nerves in much 
greater proportion to organs situated in the neck and thorax. One of these, 
the pneurno-gastric, after giving a small branch to the ear-passages, and sup- 
plying nerves to the larynx and pharynx, the trachea, gullet, the lungs 
and heart, extends into the abdominal cavity as the principal nerve of the 
stomach. The other, the spinal accessory, which is partially united with 
the gloss o-pharyngeal and pneumo-gastric near their origin and thus furnishes 
some of their motor fibres, is entirely a motor nerve, and is distributed in 
the steruo-mastoid and trapezius muscles. The glosso-pharyngeal nerve is 
more strictly confined to the head, supplying branches to the tongue, 
pharynx, and part of the ear-passages. 

On the following two pages, Fig. 400 is introduced in illustration of the general 
view of the distribution above given. In this figure the cranium and orbit have been 
opened up to the depth of the several foramina through which the nerves pass. The 
greater part of the lower jaw has also been removed on the left side, and the tongue, 
pharynx, and larynx are partially in view. The occipital bone has been divided by an 
incision passing down from the occipital tuberosity and through the condyle to the 
left of the foramen magnum. The cervical vertebrae have been divided to the left of 



590 THE CRANIAL NERVES. 

the middle, and the sheath of the spinal cord opened so as to expose the roots of the 
cervical nerves. 

Fig. 400, A. 




Fig. 400. A. SEMIDIAGRAMMATIC VIEW OF A DEEP DISSECTION OP THE CRANIAL NERVES 
ON THE LEFT SIDE OF THE HEAD (from various authors and from nature). B. EXPLANA- 
TORY OUTLINE OF THE SAME. 

The roinan numerals from I to IX indicate the roots of the several cranial nerves as 
they lie in or near their foramina of exit. V, is upon the great root of the fifth with the 
ganglion in front ; a and b, in connection with VII, indicate respectively the facial and 
auditory nerves ; a, b, and c, in connection with VIII, point respectively to the glosso- 
pharyngeal, pneumo -gas trie, and spinal accessory nerves ; C I, the suboccipital or first 
cervical nerve ; C VIII, the eighth. The branches or distributed parts of the nerves are 
marked as follows, viz. : I, frontal branch of the fifth ; 2, lachrymal passing into the gland; 
3, nasal passing towards the internal orbitary foramen and giving the long twig to the ciliary 
ganglion (4') ; 3', external branch of the internal nasal nerve ; 4, lower branch of the third 
or oculo-motor nerve ; 5, the superior maxillary division of the fifth passing into the infra- 
orbital canal ; 5', its issue at the infraorbital foramen and distribution as inferior 
palpebral, lateral nasal, and superior labial nerves (5") ; 6, ganglion of Meckel and 
Vidian nerve passing back from it ; 6', palatine and other nerves descending from it ; 6", 
superior petrosal nerve ; 7, posterior superior dental nerves ; 7', placed in the antrum 
maxillare, which has been opened, points to the anterior superior dental nerves ; 8, 
inferior maxillary division of the fifth immediately below the foramen ovale ; 8', some of 
the muscular branches coming from it ; 8 x , the anterior auricular branch cut short, and 
above it the small pstrosal nerve to join the facial nerve ; 9, buccal and internal ptery- 



GENERAL DISTRIBUTION. 



591 



gold ; 10, gustatory nerve ; 10', its distribution to the. side and front of the tongue and 
to the sublingual glands ; 10", the submaxillavy ganglion connected with the gustatory 

Fig. 400, B. 




nerve ; below 10, the chorda tympani passing back from the gustatory to join the facial 
nerve above 12 ; 11, inferior dental nerve ; 11', the same nerve and part of its dental distri- 
bution exposed by removal of the jaw ; 11", termination of the same as mental and inferior 
labial nerves ; 12, the twigs of the facial nerve to the posterior belly of the digastric and 
to the stylo-byoid muscle immediately after its exit from the stylo-mastoid foramen ; 12', 
the temporo-facial division of the facial; 12'', the cervico-facial division; 13, the trunk 
of the glosso-pharyngeal passing round the stylo- pharyngeus muscle after giving pharyngeal 
and muscular branches; 13', its distribution on the side and back part of the tongue ; 
14, the spinal accessory nerve, at the place where it crosses the ninth and gives a com- 
municating branch to the pneumo-gastric and glosso-pharyngeal nerves ; 14', the same 
nerve after having passed through the sterno-mastoid muscle uniting with branches 
from the cervical nerves; 15, ninth nerve; 15', its twig to the thyro-hyoid muscle; 
15", its distribution in the muscles of the tongue; 16, descendens noni nerve giving 
a direct branch to the upper belly of the omo-hyoid muscle, and receiving the com- 
municating branches 16 x from the cervical nerve; 17, pneumo-gastric nerve; 17', its 
superior laryngeal branch; 17", external laryngeal twig ; 18, superior cervical ganglion 
of the sympathetic nerve, uniting with the upper cervical nerves, and giving at 18' 
the superficial cardiac nerve ; 19, the trunk of the sympathetic ; 19', the middle cervical 
ganglion, uniting with some of the cervical nerves, and giving 19", the large middle 
cardiac nerve ; 20, continuation of the sympathetic nerve down the neck ; 21, great 
occipital nerve ; 22, third occipital. 



THE CRANIAL XEHVES. 



OLFACTORY NERVE. 

The olfactory or first cranial nerve, the special nerve of the sense of smell, 
is distributed exclusively to the nasal fossae. 

From the under surface of the olfactory bulb about twenty branches 
proceed through the holes in the cribriform plate of the ethmoid bone, each 
invested by tubular prolongations of the membranes of the brain. These 
tubes of membrane vary in the extent to which they are continued on the 
branches : the offsets of the dura mater sheathe the filaments, and join the 
periosteum lining the nose ; those of the pia mater become blended with 
the neurilemma of the nerves ; and those of the arachnoid re-ascend to the 
serous lining of the skull. 



Fig. 401. 




XII 



Fig. 401. DISTRIBUTION OP THE OLFACTORY NKRVES ON THE SEPTUM OF THE NOSE (from 
Sappey after Hirschfeld and Leveille). 

The septum is exposed and the anterior palatine canal opened on the right side. I, 
placed above, points to the olfactory bulb, and the remaining roman numbers to the roots 
of the several cranial nerves ; 1, the small olfactory nerves as they pass through the 
cribriform plate ; 2, internal or septal twig of the nasal branch of the ophthalmic nerve ; 
3, naso-palatine nerves. (See Fig. 408 for a view of the distribution of the olfactory 
nerves on the outer wall of the nasal fossa.) 

The branches are arranged in three sets. Those of the inner set, lodged for 
some distance in grooves on the surface of the bone, ramify in the pituitary 
membrane of the septum ; the outer set extend to the upper two spongy bones 
and the plane surface of the ethmoid bone in front of these ; and the middle 
set, which are very short, are confined to the roof of the nose. The distri- 
bution of the olfactory > nerve is confined to the upper part of the nasal 
fossa ; none of the branches reach the lower spongy bone. (See Anatomy 
of the Nose.) 

OPTIC NERVE. 

The optic or second cranial nerve, the nerve of vision, extending from 
the optic commissure, becomes more cylindrical and firm as it diverges from 
its fellow and enters the orbit by the optic foramen. Within the orbit it 
forms a cylindrical trunk, thick and strong, with a uniform surface. On dis- 



OPTIC NERVE. THIRD PAIR. 



593 



section it is seen to consist of a number of separate bundles of nerve fibres, 
imbedded in tough fibrous tissue prolonged from the dura mater, and per- 
forated in the centre by the small arteria centralis retinae, which passes into 
it soon after it enters the orbit. It is surrounded by the recti muscles, 
and, entering the eyeball posteriorly a little to the inside of its middle, it 
pierces the sclerotic and choroid coats, and expands in the retina. (See the 
Anatomy of the Eye.) 

It may be mentioned that in many fishes the optic nerves do not unite in a com- 
missure, but merely cross each to the side opposite to that of its origin ; and that 
in a number of the same animals, as was first pointed out by Malphighi, the nerve 
consists of a lamina thrown into complicated longitudinal plications, and surrounded 
by a sheath. 

THIRD PAIR OF NERVES. 

This nerve, the common motor nerve of the eyeball (motorius oculi), 
gives branches to five of the seven muscles of the orbit, viz., to the 

Fig. 402. VIEW FROM ABOVE Fig. 402. 

OF THE UPPERMOST NERVES 
OF THE ORBIT, THE GAS- 
SERIAN GANGLION, &c. (from 
Sappey after Hirschfeld and 
Leveille). | 

I, the olfactory tract passing 
forwards into the bulb ; II, the 
commissure of the optic nerves ; 
IN, the oculo-motor ; IV, the 
trochlear nerve; V, the greater 
root of the fifth nerve, a small 
portion of the lesser root is 
seen below it ; VI, the sixth 
nerve ; VII, facial ; VIII, audi- 
tory ; IX, glosso-pharyngeal ; 
X, pneumo-gastric ; XI, spinal 
accessory ; XII, hypoglossal ; 
1, the Gasserian ganglion; 2, 
ophthalmic nerve ; 3, lachrymal 
branch ; 4, frontal ; 5, external 
frontal or supraorbital ; 6, 
internal frontal ; 7, supra- 
trochlear branch ; 8, nasal 
nerve ; 9, infratrochlear branch ; 
] 0, internal nasal passing 
through the internal orbital 
foramen; 11, anterior deep 
temporal proceeding from the 
buccal nerve ; 12, middle deep 
temporal ; 13, posterior deep 
temporal arising from the 
masseteric ; 14, origin of the 
temporo-auricular ; 15, great superficial petrosal nerve. 

superior, internal and inferior straight muscles, to the levator palpebrse, and 
to the inferior oblique muscle. 

Cylindrical and firm, like the other motor nerves, the third nerve, 
quitting the investment of the arachnoid membrane, pierces the inner layer 
of the dura mater close to the posterior clinoid process, and proceeds 
towards the sphenoidal fissure, lying in the external fibrous boundary of the 
cavernous sinus. 




594 THE CRANIAL NERVES. 

After receiving one or two delicate filaments from the cavernous plexus of 
the sympathetic, the third nerve divides near the orbit into two parts, which 
are continued into that cavity between the heads of the external rectus 
muscle, and separated one from the other by the nasal branch of the 
ophthalmic nerve. 

The upper, the smaller part, is directed inwards over the optic nerve to 
the superior rectus muscle of the eye and the elevator of the eyelid, to both 
which muscles it furnishes branches. 

The lower and larger portion of the nerve separates into three branches ; 
of these one reaches the inner rectus ; another the lower rectus ; and the 
third, the longest of the three, runs onwards between the lower and the 
outer rectus, and terminates below the ball of the eye in the inferior 
oblique muscle. The last-mentioned branch is connected with the lower 
part of the lenticular ganglion by a short thick cord, and gives two filaments 
to the lower rectus muscle. 

The several branches of the third nerve enter the muscles to which they 
are distributed on the surface which in each looks towards the eyeball 

POSITION OP CERTAIN NERVES at the cavernous sinus, and as they enter the 
orbit. There are several nerves, besides the third, placed close together at 
the cavernous sinus, and entering the orbit through the sphenoidal fissure. 
To avoid repetition hereafter, the relative positions of these nerves may 
now be described. The nerves thus associated are the third, the fourth, 
the ophthalmic division of the fifth, and the sixth. 

At the cavernous sinus. In the dura mater which bounds the cavernous 
sinus on the outer side, the third and fourth nerves and the ophthalmic 
division of the fifth are placed, as regards one another, in their numerical 
order both from above downwards and from within outwards. The sixth 
nerve is placed separately from the others close to the carotid artery, 
on the floor of the sinus and internally to the fifth nerve. Near the sphe- 
noidal fissure, through which they enter the orbit, the relative position of 
the nerves is changed, the sixth nerve being here close to the rest, and 
their number is augmented by the division of the third and the ophthalmic 
nerves the former into two, the latter into three parts. 

In the sphenoidal fissure. The fourth and the frontal and lachrymal 
branches of the fifth, which are here higher than the rest, lie on the same 
level, the fourth being the nearest to the inner side, and enter the orbit 
above the muscles. The remaining nerves pass between the heads of the 
outer rectus muscle, in the following relative position to each other ; the 
upper division of the third highest, the nasal branch of the fifth next, the 
lower division of the third beneath these, and the sixth lowest of all. 

FOURTH PAIR OF NERVES. 

The fourth (nervus trochlearis, n. patheticus) is the smallest of the cranial 
nerves, and is distributed entirely to the upper oblique muscle of the 
orbit. 

From the remoteness of its place of origin, the part of this nerve within 
the skull is longer than that of any other cranial nerve. It enters an aperture 
in the free border of the tentorium, outside that for the third nerve, and 
near the posterior clinoid process. Continuing onwards through the outer 
wall of the cavernous sinus, the fourth nerve enters the orbit by the 
sphenoidal fissure, and above the muscles. Its position with reference to 
other nerves in this part of its course has been already described. 



FOURTH PAIE. 



595 



In the orbit, the fourth nerve inclines inwards above the muscles, and 
enters finally the upper oblique muscle at its orbital surface. 

While in its fibrous canal in the outer wall of the sinus, the fourth nerve is joined 
by filaments of the sympathetic, and not unfrequently is blended with the ophthalmic 



Fig. 403. VIEW FROM ABOVE OP THE MOTOR NERVES 
OF THE EYEBALL AND ITS MUSCLES (after Hirsch- 
feld and Leveille, altered). 



Fig. 403. 



The ophthalmic division of the fifth pair has been 
cut short ; the attachment of the muscles round the 
optic nerve has been opened up, and the three upper 
muscles turned towards the inner side, their anterior 
parts being removed ; a part of the optic nerve is cut 
away to show the inferior rectus ; and a part of the 
sclerotic coat and cornea is dissected off showing the 
iris, zona ciliaris, and choroid coat, with the ciliary 
nerves. 

, the upper part of the internal carotid artery 
emerging from the cavernous sinus ; 6, the superior 
oblique muscle ; &', its anterior part passing through 
the pulley ; c, the levator palpebrse superioris ; d, 
the superior rectus ; e, the internal rectus ; /, the 
external rectus; /', its upper tendon turned down ; 
gr, the inferior rectus j h, insertion of the inferior 
oblique muscle. 

II, the commissure of the optic nerve ; II', part 
of the optic nerve entering the eyeball ; III, the 
common oculo-motor ; IV, the fourth or trochlear 
nerve ; V, the greater root of the trigeminus ; V, 
the smaller or motor root ; VI, the abducent nerve ; 
1, the upper division of the third nerve separating 
from the lower and giving twigs to the levator palpe- 
brse and superior rectus ; 2, the branches of the 
lower division supplying the internal and inferior 
recti muscles ; 3, the long branch of the same nerve 
proceeding forward to the inferior oblique muscle, 
and close to the number 3, the short thick branch 
to the ciliary ganglion : this ganglion is also shown, 

receiving from behind the slender twig from the nasal nerve, which has been cut short, 
and giving forwards some of its ciliary nerves, which pierce the sclerotic coat ; 3', marks 
the termination of some of these nerves in the ciliary muscle and iris after having passed 
between the sclerotic and choroid coats ; 4, the distribution of the trochlear nerve to the 
upper surface of the superior oblique muscle ; 6, the abducent nerve passing into the 
external rectus. 

division of the fifth. Bidder states that three or more small filaments of this nerve 
extend in the tentorium as far as the lateral sinus ; and has figured one as joining the 
sympathetic on the carotid artery. (Neurologische Beobachtungen, Von F. H. Bidder. 
Dorpat, 1836.) 

FIFTH PAIR OF NERVES. 

The fifth, or trifacial nerve (nerv. trigeminus), the largest cranial nerve, 
is analogous to the spinal nerves, in respect that it consists of a motor and 
a sensory part, and that the sensory fibres pass through a ganglion while 
the motor do not. Its sensory division, which is much the larger, imparts 
common sensibility to the face and the fore part of the head, as well as to 
the eye, the nose, the ear, and the mouth ; and endows the fore part of 
the tongue with the powers of both touch and taste. The motor root 
supplies chiefly the muscles of mastication. 




596 



THE CRANIAL NERVES. 



The roots of the fifth nerve, after emerging from the surface of the 
encephalon, are directed forwards, side by side, to the middle fossa of the 
skull, through a recess in the dura mater on the summit of the petrous 
part of the temporal bone. Here the larger root alters in appearance : its 

Fig- 404. Fig. 404. GENERAL PLAN 

OP THE BRANCHES OF 
THE FIFTH PAIR (after 
a sketch by Charles 
Bell), i 

1, lesser root of the 
fifth pair ; 2, greater 
root passing forwards 
into the Gasserian gang- 
lion ; 3, placed on the 
bone above the ophthal- 
mic nerve, which is seen 
dividing into the supra- 
orbital, lachrymal, and 
nasal branches, the latter 
connected with the oph- 
thalmic ganglion ; 4, 
placed on the bone close 
to the foramen rotundum, 
marks the superior max- 
illary division, which is 
connected below with the 
spheno-palatine ganglion, 
and passes forwards to 
the infraorbital foramen ; 
5, placed on the bone over 
the foramen ovale, marks 
the submaxillary nerve, 
giving off the anterior auri- 
cular and muscular bran- 
ches, and continued by the 
inferior dental to the lower 
jaw, and by the gustatory 

to the tongue ; a, the submaxillary gland, the submaxillary ganglion placed above it in 
connection with the gustatory nerve ; 6, the chorda tympaui ; 7, the facial nerve issuing 
from the stylo-rnastoid foramen. 

fibres diverge a little, become reticulated, and enter the Gasserian ganglion. 
The smaller root passes inside and beneath the ganglion, without its nerve- 
fibres being incorporated in any way with it, and joins outside the skull the 
lowest of the three trunks which issue from the ganglion. 

The ganglion of the fifth nerve or Gasserian ganglion (ganglion semilunare), 
occupies a depression on the upper part of the petrous portion of the 
temporal bone, near the point, and is somewhat crescentic in form, the 
convexity being turned forwards. On its inner side the ganglion is joined 
by filaments from the carotid plexus of the sympathetic nerve, and, accord- 
ing to some anatomists, it furnishes from its back part filaments to the 
dura mater. 

From the fore part, or convex border of the Gasserian ganglion, proceed 
the three large divisions of the nerve. The highest (first or ophthalmic trunk) 
enters the orbit ; the second, the upper maxillary nerve, is continued forwards 
to the face, below the orbit ; and the third, the lower maxillary nerve, is 
distributed chiefly to the external ear, the tongue, the lower teeth, and the 
muscles of mastication. The first two trunks proceed exclusively from the 




FIFTH PAIR.-OPHTHALMIC NERVE. 597 

ganglion and are entirely sensory, while the third or inferior maxillary trunk, 
receiving a considerable part from the ganglion, has associated with it also 
the whole of the fibres of the motor root, and thus distributes both motor 
and sensory branches. 

OPHTHALMIC NERVE. 

The ophthalmic nerve, or first division of the fifth nerve, the smallest of 
the three offsets from the Gasserian ganglion, is somewhat flattened, about an 
inch in length, and is directed forwards and upwards to the spheuoidal 
fissure, where it ends in branches which pass through the orbit to the sur- 
face of the head and to the nasal fossse. In the skull it is contained in the 
process of the dura mater bounding externally the cavernous sinus, and is 
joined by filaments from the cavernous plexus of the sympathetic : according 
to Arnold, it gives recurrent branches to the tentorium cerebelli. It also 
frequently communicates by a considerable branch with the fourth nerve. 

Near the orbit the ophthalmic nerve furnishes from its inner side the 
nasal branch, and then divides into the frontal and lachrymal branches. 
These branches are transmitted separately through the sphenoidal fissure, and 
are continued through the orbit (after supplying some filaments to the eye 
and the lachrymal gland) to their final distribution in the nose, the eyelids, 
and the muscles and integument of the forehead. 

LACHRYMAL BRANCH. 

The lachrymal branch is external to the frontal at its origin, and is con- 
tained in a separate tube of dura mater. In the orbit it passes along the 
outer part, above the muscles, to the outer and upper angle of the cavity. 
Near the lachrymal gland, the nerve has a connecting filament with the orbital 
branch of the superior maxillary nerve ; and when in close apposition with the 
gland, it gives many filaments to that body and to the conjunctiva. Finally, 
the lachrymal nerve penetrates the palpebral ligament externally, and ends 
in the upper eyelid, the terminal ramifications being joined by twigs from 
the facial nerve. 

In consequence of the junction which occurs between the ophthalmic trunk of the 
fifth and the fourth nerve, the lachrymal branch sometimes appears to be derived 
from both these nerves. Swan considers this the usual condition of the lachrymal 
nerve. (" A Demonstration of the Nerves of the Human Body," page 36. London, 
1834.) 

FRONTAL BRANCH. 

The frontal branch, the largest division of the ophthalmic, lies, like the 
preceding nerve, above the muscles in the orbit, being situated between the 
elevator of the upper eyelid and the periosteum. About midway forwards 
in the orbit, the nerve divides into two branches, supratrochlear and supra- 
orbital. 

a. The supratrochlear branch (internal frontal) is prolonged to the inner 
angle of the orbit, close to the point at which the pulley of the upper oblique 
muscle is fixed to the orbit. Here it gives downwards a filament to connect 
it with the infratrochlear branch of the nasal nerve, and issues from the 
cavity between the orbicular muscle of the lids and the bone. In this position 
filaments are distributed to the upper eyelid. The nerve next pierces the 



598 THE CRANIAL NERVES. 

orbicularis palpebrarum and occipito-frontalis muscles, furnishing twigs to 
these muscles and the corrugator supercilii, and, after ascending on the fore- 
head, ramifies in the integument. 

6. The supraorbital branch (external frontal) passes through the supra- 
orbital notch to the forehead, and ends in muscular, cutaneous, and peri- 
cranial branches ; while in the notch it distributes palpebral filaments to the 
upper eyelid. 

The muscular branches referred to are comparatively small, and supply the corrugator 
of the eyebrow, the occipito-frontalis, and the orbicular muscle of the eyelids, joining 
the facial nerve in the last muscle. The cutaneous branches, among which two (outer 
and inner) may be noticed as the principal, are placed at first beneath the occipito- 
frontalis. The outer one, the larger, perforates the tendinous expansion of the muscle, 
and ramifies in the scalp as far back as the lambdoidal suture. The inner branch 
reaches the surface sooner than the preceding nerve, and ends in the integument over 
the parietal bone. The pericranial branches arise from the cutaneous nerve beneath 
the muscle, and end in the pericranium covering the frontal and parietal bones. 

Fig. 405. Fig. 405. NERVES OP THE OR- 

BIT FKOM THE OUTER SlDE 

t "&- "$?ifrli (from Sappey after Hirschfeld 

and Leveilld). f 

The external rectus muscle has 
been divided and turned down: 1, 
the optic nerve; 2, thetrunkof the 
third nerve; 3, its upper divisioa 
pasing into the levator palpebrae 
and superior rectus ; 4, its long 
lower branch to the inferior oblique 
muscle ; 5, the sixth or abducent 
nerve joined by twigs from the 
sympathetic ; 6, the Gasserian 

8 7 10 " -A ganglion ; 7, ophthalmic nerve ; 8, 

its nasal branch ; 9, the ophthal- 
mic ganglion ; 10, its short or 

motor root ; 11, long sensory root from the nasal nerve; 12, sympathetic twig from 
the carotid plexus ; 13, ciliary nerves passing into the eyeball ; 14, frontal branch of the 
ophthalmic nerve. 

NASAL BRANCH. 

The nasal branch (oculo-nasalis), separating from its parent trunk in the 
wall of the cavernous sinus, enters the orbit between the heads of the outer 
rectus. It then inclines inwards over the optic nerve, beneath the elevator 
of the upper eyelid and the superior rectus muscle, to the inner wall of the 
orbit, through which it passes by the anterior internal orbital foramen. In 
this oblique course across the orbit it furnishes a single filament to the 
ophthalmic ganglion, two or three (long ciliary) directly to the eyeball ; and, 
at the inner side of the cavity, a considerable branch (infratrochlear), which 
issues from the orbit at the fore part. 

On leaving the orbit the nasal nerve is directed transversely inwards to 
the upper surface of the cribriform plate of the ethmoid bone, and, passing 
forwards in a groove at its outer edge, within the cranium, descends by a 
special aperture close to the crista galli at the fore part of the plate to the 
roof of the nasal fossa, where it divides into two branches, one of which 
(external or superficial nasal) reaches the integument of the side of the nose, 
and the other (rainus septi) ramifies in the pituitary membrane. 




NASAL NERVE. OPHTHALMIC GANGLION. 599 

a. The branch to the ophthalmic ganglion (radix longa ganglii ciliaris), very slender, 
and about half an inch long, arises generally between the heads of the external 
rectus ; it lies on the outer side of the optic nerve, and enters the upper and back 
part of the ophthalmic ganglion, constituting its long root. 

This small branch is sometimes joined by a filament from the cavernous plexus of 
the sympathetic, or from the upper branch of the third nerve. 

b. The long ciliary nerves, two or three in number, are situated on the inner side 
of the optic nerve ; they join one or more of the nerves from the ophthalmic ganglion 
(short ciliary), and after perforating the sclerotic coat of the eye, are continued 
between it and the choroid to the ciliary muscle, the cornea, and the iris. 

c. The infratrochlear branch runs forwards along the inner side of the orbit below 
the superior oblique muscle, and receives near the pulley of that muscle a filament of 
connection from the supratrochlear nerve. The branch is then continued below the 
pulley to the inner angle of the eye, and ends in filaments which supply the orbicular 
muscle of the lids, the caruncula, and the lachrymal sac, as well as the integument of 
the eyelids and side of the nose. 

In the cavity of the nose the nasal nerve ends by dividing into the following 
branches. 

d. The branch to the nasal septum extends to the lower part of the partition 
between the nasal fossae, supplying the pituitary membrane near the fore part of the 
septum. 

e. The superficial branch (externus seu lateralis), descends in a groove on the inner 
surface of the nasal bone ; and after leaving the nasal cavity between that bone and 
the lateral cartilage of the nose, it is directed downwards to the tip of the nose, 
beneath the compressor naris muscle. While within the nasal fossa, this branch 
gives two or three filaments to the fore part of its outer wall, which extend as far as 
the lower spongy bone. The cutaneous part is joined by a filament of the facial 
nerve. 

Summary. The first division of the fifth nerve is altogether sensory in 
function. It furnishes branches to the ball of the eye and the lachrymal 
gland ; to the mucous membrane of the nose and eyelids ; to the integument 
of the nose, the upper eyelid, the forehead, and the upper part of the hairy 
scalp ; and to the muscles a'bove the middle of the circumference of the 
orbit. Some of the cutaneous and muscular filaments join branches of the 
facial nerve, and the nerve itself communicates with the sympathetic. 

OPHTHALMIC GANGLION. 

There are four small ganglia connected with the divisions of the fifth 
nerve : the ophthalmic ganglion with the first, Meckel's ganglion with the 
second, and the otic and submaxillary ganglia with the third. These 
ganglia, besides receiving branches from the sensory part of the fifth, are 
each connected with a motor nerve from the third, the fifth, or the facial, 
and with twigs from the sympathetic ; and the nerves thus joining the 
ganglia are named their roots. 

The ophthalmic or lenticular ganglion (gang, semilunare, vel ciliare) serves 
as a centre for the supply of nerves motor, sensory, and sympathetic to 
the eyeball. It is a small reddish body, situated at the back of the orbit, 
between the outer rectus muscle and the optic nerve, and generally in contact 
with the ophthalmic artery ; it is joined behind by branches from the fifth, 
the third, and the sympathetic nerves ; while from its fore part proceed the 
ciliary nerves to the eyeball. 

Union of the ganglion with nerves : its roots. The posterior border of the 
ganglion receives three nerves. One of these, the long root, a slender 
filament from the nasal branch of the ophthalmic trunk, joins the upper 
part of this border. Another branch, the short root y much thicker and 
shorter than the preceding, and sometimes divided into parts, is derived 



600 THE CRANIAL NERVES. 

from the branch of the third nerve to the inferior oblique muscle, and is 
connected with the lower part of the ganglion. The third root is a very 
small nerve which emanates from the cavernous plexus of the sympathetic, 
and reaches the ganglion with the long upper root : these two nerves are 
sometimes conjoined before reaching the ganglion. Other roots have been 
assigned to the ganglion. (Valentin, in Miiller's Archiv. for 1840.) 

Brandies of the ganglion. From the fore part of the ganglion arise ten 
or twelve delicate filaments the short ciliary nerves. These nerves are 
disposed in two fasciculi, arising from the upper and lower angles of the 
ganglion, and they run forwards, one set above, the other below the optic 
nerve, the latter being the more numerous. They are accompanied by fila- 
ments from the nasal nerve (long ciliary), with which some are joined. Having 
entered the eyeball by apertures in the back part of the sclerotic coat, the 
nerves are lodged in grooves on its inner surface ; and at the ciliary muscle, 
which they pierce (some filaments supplying it and the cornea), they turn 
inwards and ramify in the iris. 



SUPERIOR MAXILLARY NERVE. 

The superior maxillary nerve, or second division of the fifth cranial nerve, 
is intermediate in size between the ophthalmic and the inferior maxillary 
trunks. 

It commences at the middle of the Gasserian ganglion, and, passing hori- 
zontally forwards, soon leaves the skull by the foramen rotuudum of the 
sphenoid bone. The nerve then crosses the spheno-maxillary fossa, and 
enters the infraorbital canal of the upper maxilla, by which it is conducted 
to the face. After emerging from the infraorbital foramen, it terminates 
beneath the elevator of the upper lip in branches which spread out to the 
side of the nose, the eyelid, and the upper lip. 

Branches. In the spheno-maxillary fossa a temporo-malar branch 
ascends from the superior maxillary nerve to the orbit, and two spheno- 
palatine branches descend to join Meckel's ganglion. Whilst the nerve is 
in contact with the upper maxilla, it furnishes two posterior dental branches 
on the tuberosity of the bone, and an anterior dental branch at the fore part. 
On the ace are the terminal branches already indicated. 

ORBITAL BRANCH. 

The orbital or temporo-malar branch, a small cutaneous nerve, enters the 
orbit by the spheno-maxillary fissure, and divides into two branches 
(temporal and malar), which pierce the malar bone, and are distributed to 
the temple and the prominent part of the cheek. 

a. The temporal branch is contained in an osseous groove or canal in the 
outer wall of the orbit, and leaves this cavity by a foramen in the malar 
bone. When about to traverse the bone, it is joined by a communicating 
filament (in some cases, two filaments) from the lachrymal nerve. The 
nerve is then inclined upwards in the temporal fossa between the bone and 
the temporal muscle, perforates the aponeurosis over the muscle an inch 
above the zygoma, and ends in cutaneous filaments over the temple. The 
cutaneous ramifications are united with the facial nerve, and sometimes 
with the superficial temporal nerve of the third division of the fifth. 

6. The malar branch lies at first in the loose fat in the lower angle of the 
orbit, and is continued to the face through a foramen in the fore part of 



SUPERIOR MAXILLARY NERVE. 601 

the malar bone, where it is frequently divided into two filaments. In the 
prominent part of the cheek this nerve communicates with the facial nerve. 

Fig. 406. 




Fig. 406. SUPERIOR MAXILLARY NERVE AND SOME OF THE ORBITAL NERVES (from 
Sappey after Hirschfeld and Leveille). 3 

1, the Gasserian ganglion ; 2, lachrymal branch of the ophthalmic nerve; 3, trunk of the 
superior maxillary nerve ; 4, its orbital branch, joining at 5, the palpebral twig of the 
lachrymal ; 6, origin of its malar twig ; 7, its temporal twig ; 8, spheno-palatine ganglion ; 
9, Vidian nerve ; 10, its upper branch or great superficial petrosal nerve proceeding to join 
the facial nerve (11) ; 12, union of the lower branch of the Vidian nerve with the carotid 
branch of the sympathetic ; 13, 14, posterior dental nerves ; 15, terminal branches of the 
infrnorbital nerves ramifying on the side of the nose and upper lip ; 16, a branch of the 
facial uniting with some of the twigs of the infraorbital. 

POSTERIOR DENTAL BRANCHES. 

The posterior dental branches, two in number, are directed downwards 
and outwards over the back part and tuberosity of the maxillary bone. 

One of the branches enters a canal in the bone by which it is conducted 
to the teeth, and gives forwards a communicating filament to the anterior 
dental nerve. It ends in filaments to the molar teeth and the lining mem- 
brane of the maxillary sinus, and near the teeth joins a second time with 
the anterior dental nerve. 

The anterior of the two branches, lying on the surface of the bone, is 
distributed to the gums of the upper jaw and to the buccinator muscle. 

ANTERIOR DENTAL BRANCH. 

The anterior dental branch, leaving the trunk of the nerve at a varying 
distance behind its exit from the infraorbital foramen, enters a special canal 
in front of the antrum of Highmore. In this canal it receives the com- 
municating filament from the posterior dental nerve, and divides into two 
branches, which furnish offsets for the front teeth. 

(a) The inner branch supplies the incisor and canine teeth. Filaments from this 
nerve enter the lower meatus of the nose, and end in the membrane covering the 
lower spongy bone. Also above the root of the canine tooth, it unites with a branch of 
the posterior nasal nerve from Meckel's ganglion, and forms with it a small thickening, 



602 THE CRAXIAL NERVES. 

the ganglion of Bochdalcl, from which branches are described as descending to the 
alveolar process and gums of the incisor and canine teeth. (See Hyrtl's Lehrbuch, 
p. 804.) 

(b) The outer branch gives filaments to the bicuspid teeth, and is connected with 
the posterior dental nerve. 

TNFRAORBTTAL BRANCHES. 

The infraorbital branches, large and numerous, spring from the end of 
the superior maxillary nerve beneath the elevator muscle of the upper lip, 
and are divisible into palpebral, nasal, and labial sets. 

Fig. 407. 




Fig. 407. DEEP VIEW OP THE SpnENo-PALATiNE GANGLION, AND ITS CONNECTIONS WITH 
OTHEK NEKVES, &c. (from Sappey after Hirschfeld and Leveille). f 

1, superior maxillary nerve ; 2, posterior superior dental ; 3, second posterior dental 
branch ; 4, anterior dental ; 5, union of these nerves ; 6, spheno-palatine ganglion ; 7, 
Vidian nerve ; 8, its great superficial petrosal t ranch ; 9, its carotid branch ; 10, a part 
of the sixth nerve, receiving twigs from the carotid plexus of the sympathetic ; 11, superior 
cervical sympathetic ganglion ; 12, its carotid branch ; 13, trunk of the facial nerve near 
the knee or bend at the hiatus Fallopii : 14, glosso-pharyngeal nerve ; 15, anastomosing 
branch of Jacobson ; 16, twig uniting it to the sympathetic : 17, filament to the fenestra 
rotunda ; 18, filament to the Eustachian tube ; 19, filament to the fenestra ovalis ; 20, 
external deep petrosal nerve uniting with the lesser superficial petrosal ; 21, internal deep 
petrosal twig uniting with the great superficial petrosal. 

a. The palpebral branch (there are sometimes two branches) turns upwards to the 
lower eyelid in a groove or canal of the bone, and supplies the orbicular muscle ; it 
ends in filaments which are distributed to the eyelid in its entire breadth. At the 
outer angle of the eyelids this nerve is connected with the facial nerve. 

b. The nasal branches, directed inwards to the muscles and integument of the side 
of the nose, communicate with the cutaneous branch of the nasal nerve. 

c. The labial, the largest of the terminal branches of the upper maxillary nerve, 
and three or four in number, are continued downwards beneath the proper elevator 
of the upper lip. Eamifying as they descend, these nerves are distributed to the 
integument, the mucous membrane of the mouth, the labial glands, and the muscles 
of the upper lip. 

Near the orbit the infraorbital branches of the superior maxill try nerve 
are joined by considerable branches of the facial nerve, the union between 
the two being named infraorbital plexus. 



SPHENO-PALAT1NE GANGLION. 603 



SPHENO-PALATINE GANGLION". 

The splieno-palatine ganglion, frequently named Meckel's ganglion, is 
deeply placed in the spheno-maxillary fossa, close to the spheno-palatine 
foramen. It receives the two spheno-palatine branches, which descend 
together from the superior maxillary nerve as it crosses the top of the fossa. 
It is of a greyish colour, triangular in form, and convex on the outer 
surface. The grey or ganglionic substance does not involve all the fibres 
of the spheno-palatiue branches of the upper maxillary nerve, but is placed 
at the back part, at the point of junction of the sympathetic or deep 
branch of the Vidian, so that the spheuo-palatine nerves proceeding to the 
nose snd palate pass to their destination without being incorporated with 
the gangliouic mass. 

Branches proceed from the ganglion upwards to the orbit, downwards to 
the palate, inwards to the nose, and backwards through the Vidian and 
pterygo-palatine canals. 

ASCENDING BRANCHES. There are three or more very small twigs, 
which reach the orbit by the spheno-maxillary fissure, and are distributed to 
the periosteum. 

Bock describes a branch ascending from the ganglion to the sixth nerve; Tiede- 
mann, one to the lower angle of the ophthalmic ganglion. The filaments described 
by Hirzel as ascending to the optic nerve, most probably join the ciliary twigs which 
surround that nerve. 

DESCENDING BRANCHES. These are three in number, the large, the 
small, and the external palatine nerves, and are continued chiefly from 
the spheno-palatine branches of the superior maxillary. They are distri- 
buted to the tonsil, the hard and soft palate, the gums, and the mucous 
membrane of the nose. 

a. The larger or anterior palatine nerve descends in the palato-maxillary canal, 
and divides in the roof of the mouth into branches, which are received into grooves 
in the hard palate, and extend forwards nearly to the incisor teeth. In the mouth it, 
supplies the gums, the glandular structure and the mucous membrane of the hard 
palate, and joins in front with the naso-palatine nerve. When entering its canal, 
this palatine nerve gives a nasal branch which ramifies on the middle and lower 
spongy bones ; and a little before leaving the canal, another branch is supplied to 
the membrane covering the lower spongy bone : these are inferior nasal branches. 
Opposite the lower spongy bone springs a small branch, which is continued to the 
soft palate in a separate canal behind the trunk of the nerve. 

1). The smaller or posterior palatine branch, arising near the preceding nerve, 
enters with a small artery the lesser palatine canal, and is conducted to the soft 
palate, the tonsil, and the uvula. According to Meckel, it supplies the levator 
palati muscle. 

c. The external palatine nerve, the smallest of the series, courses between the 
upper maxilla and the external pterygoid muscle, and enters the external palatine 
canal between the maxillary bone and the pterygoid process of the palate bone. At 
its exit from the canal it gives inwards a branch to the uvula, and outwards another 
to the tonsil and palate. Occasionally, this nerve is altogether wanting. 

INTERNAL BRANCHES. These consist of the naso-palatine, and the upper 
and anterior nasal, which ramify iii the lining membrane of the nasal fossae 
and adjoining sinuses. 

The upper nasal are very small branches, and enter the back part of the nasal 
fossa by the spheno-palatine foramen. Some are prolonged to the upper and 
posterior part of the septum, and the remainder ramify in the membrane covering 

it R 2 



604 



THE CRANIAL NERVES. 



the upper two spongy bones, and in that lining the posterior ethmoid cells. A 
branch, as has been already stated, forms a connection in the wall of the maxillary 
sinus, above the eye-tooth, with the anterior dental nerve. 

The naso-palatine nerve, nerve of Cotunnius (Scarpa), long and slender, leaves the 
inner side of the ganglion with the preceding branches, and after crossing the roof of 
the nasal fossa is directed downwards and forwards on the septum nasi, towards the 
anterior palatine canal, situated between the periosteum and the pituitary membrane. 
The nerves of opposite sides descend to the palate through the mesial subdivisions of 
the canal, called the foramina of Scarpa, the nerve of the right side usually behind 
that of the left. In the lower common foramen the two naso-palatine nerves are 
connected with each other ; and they end in several filaments, which are distributed 
to the papilla behind the incisor teeth, and communicate with the great palatine 
nerve. In its course along the septum, small filaments are furnished from the naso- 
palatine nerve to the pituitary membrane. (See Fig 402. This nerve was discovered 
independently by John Hunter and Cotunnius ; see Hunter's " Observations on 
certain parts of the Animal Economy;" and Scarpa, "Annotationes Anatomicse," 
lib. ii.) 

Fig. 408. 




Fig. 408. NEIIVKS OP THE NOSE AND OF THE SPHENO-PALATINE GANGLION FROM THR 
INNER SIDE (from Sappey after Hirschftld and Leveille). f 

1, network of the branches of the olfactory nerve descending upon the membrane 
covering the superior and middle turbinated bones ; 2, external twig of the ethinoidal branch 
of the nasal nerve ; 3, spheno-palatine ganglion ; 4, ramification of the anterior division 
of the palatine nerves ; 5, posterior, and 6, middle divisions of the palatine nerves; 7, 
branch to the membrane on the lower turbinated bone ; 8, branch to the superior and 
middle turbinated bones ; 9, naso-palatine branch to the septum cut short ; 10, Vidian 
nerve ; 11, its great superficial petrosal branch; 12, its carotid branch; 13, the sympa- 
thetic nerves ascending on the internal carotid artery. 

POSTERIOR BRANCHES. The brandies directed backwards from the splieno- 
palatine ganglion are the Vidian aud pharyngeal nerves. 

The Vidian nerve arises from the back part of the ganglion, which seems to be pro- 
longed into it, passes backwards through the Vidian canal, and after emerging from 
this divides in the substance of the fibro-cartilage filling the foramen lacerum 
medium, into two branches : one of these, the superficial petrosal, joins the facial 
nerve, while the other, the carotid branch, communicates with the sympathetic. 
Whilst the Vidian nerve is in its canal, it gives inwards some small nasal branches, 
which supply the membrane of the back part of the roof of the nose and septum, as 
well as the membrane covering the end of the Eustachian. tube. 



INFERIOR MAXILLARY NERVE. 605 

The large superficial petrosal branch of the Vidian nerve, entering the cranium on 
the outer side of the carotid artery and beneath the Gasserian ganglion, is directed 
backwards in a groove on the petrous portion of the temporal bone to the hiatus 
Fallopii, and is thus conducted to the aqueductus Fallopii, where it joins the gangli- 
form enlargement of the facial nerve. 

The carotid or sympathetic portion of the Vidian nerve, shorter than the other, is 
of a reddish colour and softer texture : it is directed backwards, and on the outer 
side of the carotid artery ends in the filaments of the sympathetic surrounding that 
vessel. 

In accordance with the view taken of the ganglia connected with the fifth nerve 
(p. 599), the superficial petrosal and carotid parts of the Vidian nerve may be regarded 
as the motor and sympathetic roots respectively of the spheno-palatine ganglion; the 
spheno-palatiue being its sensory root. 

The pharyngeal nerve is inconsiderable in size, and, instead of emanating directly 
from the ganglion, is frequently derived altogether from the Vidian. This branch, when 
a separate nerve, springs from the back of the ganglion, enters the ptery go-palatine 
canal with an artery, and is lost in the lining membrane of the pharynx behind the 
Eustachian tube. 

Summary. The superior maxillary nerve, with Meckel's ganglion, supplies 
the integument above the zygomatic arch, and that of the lower eyelid, the 
side of the nose, and the upper lip ; the upper teeth, the lining mem- 
brane of the nose ; the membrane of the upper part of the pharynx, of the 
antrum of Highmore, and of the posterior ethmoid cells ; the soft palate, 
tonsil, and uvula ; and the glandular and mucous structures of the roof of 
the mouth. 

INFERIOR MAXILLARY NERVE. 

The lower maxillary nerve, the third and largest division of the fifth 
nerve, is made up of two portions, unequal in size, the larger being derived 
from the Gasserian ganglion, aud the smaller being the slender motor root 
of the fifth nerve. These two parts leave the skull by the foramen ovale 
in the sphenoid bone, and unite immediately after their exit. A few lines 
beneath the base of the skull, and under cover of the external pterygoid 
muscle, the nerve separates into two primary divisions, one of which is 
higher in position and smaller than the other. 

The small, anterior or upper portion, purely motor, terminates in 
branches to the temporal, masseter, buccinator, and pterygoid muscles. The 
larger or lower portion, chiefly sensory, divides into the auriculo-temporal, 
gustatory, and inferior dental branches : it likewise supplies the mylohyoid 
muscle, and the anterior belly of the digastric. The branch to the in- 
ternal pterygoid muscle, with which also are connected those proceeding 
from the otic ganglion to the tensors of the palate and tympanum, is 
sometimes counted as a part of the larger division, but is more correctly 
regarded as arising from the undivided trunk. 

DEEP TEMPORAL, MASSETERIC, BUCCAL, AND PTERYGOID BRANCHES. 

The deep temporal branches, two in number, anterior and posteriory pass 
outwards above the external pterygoid muscle, close to the bone, and run 
upwards, one near the front, and the other near the back of the tem- 
poral fossa, beneath the temporal muscle in the substance of which they 
are distributed. (See fig. 403.) 

The anterior branch is frequently joined with the buccal nerve, and 
sometimes with the other deep temporal branch. 

The masseteric branch likewise passes above the external pterygoid 



606 THE CRANIAL NERVES. 

muscle, and is directed nearly horizontally outwards through the sigmoid 
notch of the lower jaw to the posterior border of the masseteric muscle, 
which it enters on the deep surface. It gives a filament or two to the 
articulation of the jaw, and occasionally furnishes a branch to the tem- 
poral muscle. 

The buccal branch pierces the substance of the external pterygoid muscle, 
and courses downwards and forwards to the face, in close contact with the 
deep surface of the temporal muscle at its insertion. It furnishes a branch 
to the external pterygoid muscle as it pierces it, and on emerging gives 
two or three ascending branches to the temporal muscle. It divides into 
two principal branches, an upper and a lower, which communicate with the 
facial nerve in a plexus round the facial vein, and are distributed to the 
integument, the buccinator muscle, and the mucous membrane. 

The external pterygoid branch, is most frequently derived from the buccal 
nerve. It is sometimes a separate offset from the smaller portion of the 
lower maxillary nerve. 

The nerve of the internal pterygoid muscle is closely connected at its 
origin with the otic ganglion, and enters the inner or deep surface of the 
muscle. 

AURICFLO-TEMPORAL NERVE. 

The auriculo-temporal nerve takes its origin close to the foramen ovale. It 
often commences by two roots, Between which may be placed the middle 
meningeal artery. It is directed at first backwards, beneath the external 
pterygoid muscle, to the inner side of the articulation of the jaw ; then 
changing its course, it turns upwards betwt ea the ear and the joint, covered 
by the parotid gland ; and emerging from this place, it finally divides iuto 
two temporal branches which ascend towards the top of the head. 

(a) Communicating branches. There are commonly two branches which pass 
forward round the external carotid artery, and join the facial nerve. Filaments to 
the otic ganglion arise near the beginning of the nerve. 

(b) Parotid branches are given from the nerve while it is covered by the gland. 

(c) Auricular branches. These are two in number. The lower of the two, arising 
behind the articulation of the jaw, distributes branches to the ear below the external 
meatus; and sends other filaments round the internal maxillary artery to join the 
sympathetic nerve ; the upper branch, leaving the nerve in front of the ear, is dis- 
tributed in the integument covering the tragus and the pinna above the external 
auditory meatus. Both are confined to the outer surface of the ear. 

(d) Branches to the meatus auditorius. These, two in number, spring from the 
point of connection of the facial and auriculo-temporal nerves, and enter the interior 
of the auditory meatus between the osseous and cartilaginous parts. One of them 
sends a branch to the membrana tympani. 

(e) Articular branch. The nerve to the temporo-maxillary articulation comes 
from one of the preceding branches, or directly from the auriculo-temporal nerve. 

(/) Temporal branches. One of these, the smaller and posterior of the two, 
distributes filaments to the anterior muscle of the auricle, the upper part of the 
pinna and the integument above it. The anterior temporal branch extends with 
the superficial temporal artery to the top of the head, and ends in the integument. 
It is often united with the temporal branch of the upper maxillary nerve. Meckel 
mentions a communication between this branch and the occipital nerve. 

GUSTATORY NERVE. 

The gustatory nerve, or lingual branch of the fifth, descends under 
cover of the external pterygoid muscle, lying to the inner side and in 



GUSTATORY XERVE. 



607 



front of the dental nerve, and sometimes united to it by a cord which 
crosses over the internal maxillary artery. It is there joined at an acute 
angle by the chorda tympani, a small branch connected with the facial 
nerye, which descends from the inner end of the Glasserian. fissure. It 
then passes between the internal pterygoid muscle and the lower maxilla, 
and is inclined obliquely inwards to the side of the tongue, over the 
upper constrictor of the pharynx, (where this muscle is attached to the 
maxillary bone,) and above the deep portion of the submaxiliary gland. 
Lastly, the nerve crosses Wharton's duct, and is continued along the si<le 
of the tongue to the apex, in contact with the mucous membrane of the 
mouth. 

(a) Communicating branches are given to the submaxiliary ganglion, at the place 

Fig. 409. 







Fig. 409. VIEW OF THE BRANCHES OP THE INFERIOR MAXILLARY NERVE FROM THE 
OUTER SIDE (from Sapoej after Hirschfeld and Leveille). f 

The zygoma and ram us of the jaw have been removed, and the outer plate of the jaw 
taken off so as t<i open up the dental canal ; the lower part of the temporal muscle has 
been dissected off the bone, and the inasseter muscle turned down. 

1, Masseteric branch, descending to the deep surface of the muscle ; 2, a twig to the 
temporal muscle ; 5, anterior, and 7, posterior deep temporal nerves ; 3, buccal ; 4, its 
union with the facial ; 6, filaments given by the buccal to the external pterygoid muscle ; 
8, auriculo-temporal nerve ; 9, its temporal branches; 10, its anterior auricular branches ; 
11, its union witli the facial ; 12, gustatory or lingual nerve ; 13, raylo-hyoid nerve ; 14, 
inferior dental nerve ; 15, its twigs supplied to the teeth; 16, mental branches; 17, branch 
of the facial uniting with the mental. 



608 THE CRANIAL NERVES. 

where the nerve is in contact with the submaxillary gland. Others form a plexus 
with branches of the hypoglossal nerve at the inner border of the hyo-glossus muscle. 

(6) Branches to the mucous membrane of the mouth are given from the nerve at 
the side of the tongue, and supply also the gums. Some delicate filaments are like- 
wise distributed to the substance of the sublingual gland. 

(c) The lingual or terminal branches perforate the muscular structure of the tongue, 
and divide into filaments, which are continued almost vertically upwards to the conical 
and fungiform papillae. Near the tip of the tongue the branches of the gustatory and 
hypoglossal nerves are united. 

INFERIOR DENTAL NERVE. 

The inferior dental nerve is the largest of the three branches of the 
lower maxillary nerve. It descends under cover of the external pterygoid 
muscle, behind and to the outer side of the gustatory nerve, and, passing 
between the ramus of the jaw and the internal lateral ligament of the 
temporo-maxillary articulation, enters the inferior dental canal. In com- 
pany with the dental artery, it proceeds along this canal, and supplies 
branches to the teeth. At the mental foramen it bifurcates ; one part, 
the incisor branch, being continued onwards within the bone to the 
middle line, while the other, the much larger labial branch, escapes by the 
foramsn to the face. 

When about to enter the foramen on the inner surface of the ramus of 
the jaw, the inferior dental nerve gives off the slender rnylo-hyoid branch. 

(a) The mylo-hyoid branch is lodged in a groove on the inner surface of the ramus 
of the maxillary bone, in which it is confined by fibrous membrane, and is distributed 
to the lower or cutaneous surface of the mylo-hyoideus and to the anterior belly of 
the digastric muscle. This nerve may be traced back within the sheath of the inferior 
dental to the motor portion of the inferior maxillary nerve. 

(b) The dental branches supplied to the molar and bicuspid teeth correspond to the 
number of the fangs of those teeth. Each branch enters the minute foramen in the 
extremity of a fang, and terminates in the pulp of the tooth. Not unfrequently a 
collateral branch supplies twigs to several teeth. 

(c) The incisor branch has the same direction as the trunk of the nerve : it extends 
to the middle line from the point of origin of the labial branch, and supplies nerves 
to the canine and incisor teeth. 

(d) The labial or mental branch emerging from the bone by the foramen on the 
outer surface, divides beneath the depressor of the angle of the mouth into two 
parts. 

One of these, the outer division, communicating with the facial nerve, supplies the 
depressor anguli oris and orbicularis oris muscles, and the integument of the chin. 

The inner portion, the larger of the two, ascends to the lower lip beneath the de- 
pressor labii inferioris muscle, to which it gives filaments : the greater number of the 
branches end on the inner and outer surfaces of the lip. These inner branches assist 
only slightly in forming the plexus of union with the facial nerve. 

OTIC GANGLION. 

The otic ganglion, or ganglion of Arnold, of a reddish grey colour, is 
situated on the deep surface of the lower maxillary trunk, nearly at the 
point of junction of the motor fasciculus with that nerve, and around the 
origin of the internal pterygoid branch. Its inner surface is close to the 
cartilaginous part of the Eustachian tube and the circumflexus palati 
muscle ; and behind it is the middle meuingeal artery. 

Connection with nerves roots. The ganglion is connected with the 
lower maxillary nerve, especially with the branch furnished to the internal 
pterygoid muscle, and with the auricnlo-teinporal nerve, and thus obtains 
motor and sensory roots ; it is brought into connection with the sympa- 



OTIC AND SUBMAXILLARY GANGLIA. 



609 



thetic by a filament from the plexus on the middle meningeal artery. 
It likewise receives the small superficial petroaal nerve, which emerges 
from the petrous bone by the small foramen internal to the canal of the 
tensor tympani muscle, and reaches the exterior of the skull by piercing 
the sphenoid bone close to the foramen spinosum. By this nerve the 
ganglion forms a communication with the glosso-pharyngeal and facial 
nerves. 

Fig. 410. OTIC GANGLTOV Fig. 410. 

AKD ITS CONNECT ONS 
FKOM THE INSIDE ( lorn 
Sappey after Arnold). 

This figure exhibits a 
view of the lateral portion 
of the skull with a part of 
the nasal fossa and lower 
jaw of the right side ; the 
petrous bone has been re- 
moved so as to show the 
inner surface of the mein- 
brana tympani and the 
canal of the facial nerve. 

1, smaller motor root of 
the fifth nerve passing 
down on the inside of the 
Gasserian ganglion to unite 
with the inferior maxillary 
division; 2, inferior denial 
nerve entering the canal of 
the lower jaw ; 3, njylo- 
hyoid branch, seen also 
farther down emerging m 
front of the internal ptery- 
goid muscle ; 4, lingual or gustatory nerve ; 5, chorda tympani ; 6, facial nerve in its 
canal ; 7, auriculo-temporal nerve, enclosing in its loop of origin the middle meningeal 
artery; 8, otic ganglion; 9, small superficial petrosal nerve joining the ganglion ; 10, 
branch to the tensor tympani muscle ; 11, twig connecting the ganglion with the temporo- 
auricular nerve ; 12, twig to the ganglion from the sympathetic nerves on the meningeal 
artery ; 13, branch to the internal pterygoid muscle ; 14, branch to the tensor palati 
muscle. 

Branches. Two small nerves are distributed to muscles one to the 
tensor of the membrane of the tympanum, the other to the circumflexus or 
tensor palati. 

SUBMAXILLARY GANGLION. 

The submaxillary ganglion is placed above the deep portion of the sub- 
maxillary gland, and is connected by filaments with the gustatory nerve. 
It is about the size of the ophthalmic ganglion. By the upper part or 
base it receives branches from nerves which may be regarded as its roots, 
whilst from the lower part proceed the filaments which are distributed from 
the ganglion. 

Connection with nerves roots. This ganglion receives filaments from 
the gustatory nerve, and likewise, at its back part, a root which appa- 
rently comes from the gustatory nerve, but is in reality derived from the 
chorda tympani, which is prolonged downwards in the sheath of the 
gustatory nerve. It receives also small twigs from the sympathetic filaments 
on the facial artery. 

Branches. Some nerves, five or six in number, radiate to the substance 




610 THE CRANIAL NERVES. 

of the submaxillary gland. Others from the fore part of the ganglion, 
longer and larger than the preceding, end in the mucous membrane of the 
mouth, and iu Whartou's duct. 

According to Meckel (" De quinto pare," &c ), a branch occasionally descends in 
front of the hyo-glossus muscle, and after joining with one from the hypoglossal nerve, 
ends in the genio-hyo-glossus muscle. 

It may be noticed that while the branches from the otic ganglion 
pass exclusively to muscles, the submaxillary ganglion gives no muscular 
offsets. 

Summary. Cutaneous filaments of the inferior maxillary nerve ramify on 
the side of the head, and the external ear, in the auditory passage, the 
lower lip, and the lower part of the face ; sensory branches are supplied 
by it to the greater part of the tongue ; and branches are furnished to the 
mucous membrane of the mouth, the lower teeth and gams, the salivary 
glands, and the articulation of the lower jaw. 

This nerve supplies the muscles of mastication, viz., the masseter, tem- 
poral, and two pterygoid ; also the buccinator, the mylo-hyoid, and the 
anterior belly of the digastric ; and from the otic ganglion proceed the 
branches to the circumflexus ]_ alati and tensor timpani muscles. 

SIXTH PAIR OF NERVES. 

The sixth cranial nerve (nerv. abducens) enters the dura mater behind 
the dorsum sellae, and passing forwards in the floor of the cavernous sinus, 
close to the outer side of the carotid artery, enters the orbit through the 
sphenoid al fissure, and between the heads of the external rectus muscle, 
and is entirely distributed to that muscle, piercing it on the ocular surface. 
In entering the orbit between the heads of the external rectus muscle, it is 
beneath the other nerves, but above the ophthalmic vein. While passiiig 
along the internal carotid artery in the cavernous sinus, it is joined by several 
filaments of the sympathetic from the carotid plexus. According to 
Bock, it is joined iu the orbit by a filament from Meckel's ganglion. 
(" Beschreibuug des Funfteu Nervenpaares." 1817.) 

SEVENTH PAIR OF NERVES. 

In the seventh cranial nerve of Willis are comprised two nerves having 
a distinct origin, distribution, and function. One of these, the facial, is the 
motor nerve of the face ; the other, the auditory, is the special nerve of the 
organ of hearing. Both enter the internal auditory meutus in the tem- 
poral bone, but they are soon separated from each other. 

FACIAL NERVE. 

The facial nerve, or portio dura of the seventh pair, is inclined outwards 
with the auditory nerve, from its place of origin, to the internal auditory 
meatus. The facial lies in a groove on the auditory nerve, and the tAvo are 
united in the auditory meatus by one or two small filaments. At the bot- 
tom of the meatus the facial nerve enters the aqueduct of Fallopius, and 
follows the windings of that canal to the lower surface of the skull. The 
nerve passes through the temporal bone at first almost horizontally outwards, 
between the cochlea and vestibule ; on reaching the inner wall of the tyrn- 



FACIAL NERVE. 



611 



pan urn it is turned suddenly backwards above the fenestra ovalis towards the 
pyramid. At the place where it bends, the nerve presents a reddish gangli- 
furm enlargement, sometimes called the geniculate ganglion, which marks the 
place of junction of several nerves. Opposite the pyramid it is arched down- 
wards behind the tympanum to the stylo-inastoid foramen, by which it leaves 
the osseous canal. It is then continued forwards through the substance of 
the parotid gland, and separates iii the gland, behind the ramus of the lower 
maxilla, into two primary divisions, the temporo-facial and the cervico- 
facial, from which numerous branches spread out over the side of the head, 
the face, and the upper part of the neck, forming what is known as the 
"pes anserinus." 

\Vithin the temporal bone the facial is connected with several other 
nerves by separate branches ; and immediately after issuing from the stylo- 
mastoid foramen, it gives off three small branches, viz., the posterior 
auricular, digastric, and stylo-hyoid. 

Fig. 411. THE FACIAL NKRVB Fig. 411. 

EXPOSED IN ITS CANAL, WITH ITS 

CONNECTING BRANCHES, &c. 
(from Sappey after Hirschfeld 
and Leveille). 

The mastoid and a part of the 
petrous bone have been divided 
nearly vertically, arid the canal of 
the facial nerve opened iu its whole 
extent from the meatus internus 
to the stylo-mastoid foramen. The 
Vidian canal has also been opened 
from the outside. 1, facial nerve 
in the horizontal part of the com- 
mencement of the canal ; 2, its 
second part turning backwards ; 
3, its vertical portion ; 4, the 
nerve at its exit from the stylo- 
mastoid foramen ; 5, geniculate 
ganglion ; 6, large superficial pe- 

trosal nerve passing from this ganglion to the spheno-palatine ganglion, and joined by 
the small internal petrosal branch; 7, spheno-palatine ganglion; 8, small superficial 
petrosal nerve ; 9, chorda tympani ; 10, posterior auricular branch cut short at its origin ; 
11, branch for the digastric muscle ; 12, branch for the stylo-hyoid muscle ; 13, twig to 
the stylo-glossus muscle uniting with muscular branches of the glosso-pharyngeal nerve 
(14 and 15). 

CONNECTING BRANCHES. 

Filaments of union with the auditory nerve. In the meatus auditorius one or two 
minute filaments pass between the facial and the trunk of the auditory nerve. 

Nerves connected with the gangliform enlargement. About two lines from the 
beginning of the aqueduct of Fallopius, where the facial nerve swells into the gangli- 
form enlargement, it is joined by the large superficial petrosal branch from the Vidian 
nerve. This ganglion likewise receives a small branch from the small superficial 
petrosal nerve which unites the otic ganglion with the tympanic nerve of Jacobson. 
The nerve beyond the ganglion receives the external superficial petrosal nerve 
(Bidder), which is furnished by the sympathetic accompanying tlie middle meningeal 
artery, and enters the temporal bone by a canal external to that traversed by the 
small superficial petrosal. 

CHOKDA TYMPANI AND NERVE TO THE STAPEDIUS. 

The nerve named chorda tympani leaves the trunk of the facial while within its 
canal, and crosses the tympanum to join the gustatory nerve, along which it i> con- 




612 



THE CRANIAL NEKVES. 



ducted towards the tongue. It enters the back part of the tympanic cavity through a 
short canal emerging below the level of the pyramid, close to the ring of bone giving 
attachment to the membrane of the tympanum ; and being invested by the mucous lining 
of the cavity, it is directed forwards across the membrana tympani and the handle of 
the malleus, to an aperture at the inner end of the Glaserian fissure. It then passes 
downwards and forwards, under cover of the external pterygoid muscle, and uniting 
with the gustatory nerve at an acute angle, descends in close contact with it, and is 
partly distributed to the submaxillary ganglion and partly blended with the gustatory 
nerve in its distribution to the tongue. As this nerve crosses the tympanum, it is 
said to supply a twig to the laxator tympaui muscle. 

Fig. 412. Fig. 412. GENICULATE GANGLION OP 

THE FACIAL NERVE AND ITS CONNEC- 
TIONS FROM ABOVE (from Bidder). 

The dissection is made iu the middle 
fossa of the skull ou the right side; the 
temporal bone being removed so as to 
open the meatus iuteruus, hiatus Fal- 
lopii, and a part of the caual of the facial 
nerve, together with the cavity of the 
tympanum, a, the external ear ; b, 
middle fossa of the skull with the 
meningeal artery ramifying in it ; 1 , 
facial and auditory nerves in the meatus 
auditorius internus ; 2, large super- 
ficial petrosal nerve ; 3, small super- 
ficial petrosal nerve lying over the ten- 
sor tyrapani muscle ; 4, the external 
superficial petrosal joining sympathetic 
twigs on the meningeal artery ; 5, facial 
and chorda tympani ; b', nerves of the 
eighth pair. 

The chorda tympani is regarded by 
some anatomists as a continuation of 
the great superficial petro.sal nerve. 
According to Owen, in the horse and 
calf, the portio dura being less dense 

in structure, the Yidian branch of the fifth may be distinctly seen crossing 
the nerve after penetrating its sheath, and separating into many filaments, with 
which filaments of the seventh nerve are blended, Avhile a ganglion is formed 
by the superaddition of grey matter ; and the chorda tympani is continued partly 
from this ganglion, partly from the portio dura. (Hunter's Collected Works, vol. iv. 
p. 194, note.) 

The nerve to the stapedius muscle arises from the trunk of the facial 
opposite the pyramid, and passes obliquely inwards t j the fleshy belly of 
the muscle. 




POSTERIOR AURICULAR BRANCH. 

This branch arises close to the stylo-mastoid foramen. In front of the 
mastoid process, it divides into an auricular and an occipital portion, aud is 
connected with the great auricular nerve of the cervical plexus. It is said 
to be joined by the auricular branch of the pneumo-gastric nerve. 

a. The auricular division supplies filaments to the retrahent muscle of 
the ear, and ends in the integument on the posterior aspect of the 
auricle. 

6. The occipital branch is directed backwards beneath the small occipital 
nerve (from the cervical plexus) to the posterior part of the occipito- 



TEMPORO-FACIAL DIVISION OF THE FACIAL. 613 

frontalis muscle ; it lies close to the bone, and, besides supplying the muscle, 
gives upwards filaments to the integument. 

DIGASTRIC AND STYLO-HYOID BRANCHES. 

The digastric branch arises in common with that for the stylo -hyoid 
muscle, and is divided into numerous filaments, which enter the digastric 
muscle : one of these sometimes perforates the digastric, and joins the 
glospo-pharyngeal nerve near the base of the skull. 

The stylo-hyoid branch, long and slender, is directed inwards from the 
digastric branch .to the muscle from which it is named. This nerve is 
connected with the plexus of the sympathetic on the external carotid 
artery. 

TEMPORO-FACIAL DIVISION. 

The temporo-facial, the larger of the two primary divisions into which 
the main trunk of the facial nerve separates, is directed forwards through 
the parotid gland. Its ramifications and connections with other nerves form 
a network over the side of the face, extending as high as the temple and 
as low as the mouth. Its branches are arranged in temporal, malar, and 
infraorbital sets. 

(a) The temporal branches ascend over the zygoma to the side of the head. Some 
end in the anterior muscle of the auricle and the integument of the temple, and 
communicate with the temporal branch of the upper maxillary nerve near the ear, as 
well as with (according to Meckel) the auriculo-temporal branch of the lower maxil- 
lary nerve. Other branches enter the occipito-frontalis, the orbicularis palpebrarum, 
and the corrugator supercilii muscles, and join offsets from the supraorbital branch 
of the ophthalmic nerve. 

(b) The malar bran' lies cross the malar bone to reach the outer side of the orbit, and 
supply the orbicular muscle. Some filaments are distributed to both the upper and 
lower eyelids : those in the upper eyelid join filaments from the lachrymal and, 
supraorbital nerves ; and those in the lower lid are connected with filaments from the 
upper maxillary nerve. Filaments from this part of the facial nerve communicate 
with the malar branch of the upper maxillary nerve. 

(c) The infraorbital brandies, of larger size than the other branches, are almost 
horizontal in direction, and are distributed between the orbit and mouth. They 
supply the buccinator and orbicularis oris muscles, the elevators of the upper lip and 
angle of the mouth, and likewise the integument. Numerous communications take 
place with the fifth nerve. Beneath the elevator of the upper lip these nerves are 
united in a plexus with the branches of the upper maxillary nerve ; on the side of 
the nose they communicate with the nasal, and at the inner angle of the orbit with 
the infratrochlear nerve. The lower branches of this set are connected with those of 
the cervico-facial division. 

Near its commencement the temporo-facial division of the facial is connected with 
the auriculo-temporal nerve of the fifth, by one or two branches of considerable size 
which turn round the external carotid artery; and it gives some filaments to the 
tragus of the outer ear. 

CERVICO-FACIAL DIVISION. 

This division of the facial nerve is directed obliquely through the parotid 
gland towards the angle of the lower jaw, and gives branches to the face, 
below those of the preceding division, and to the upper part of the neck. 
The branches are named buccal, supramaxillary, and inframaxillary. In the 
gland, this division of the facial nerve is joined by filaments of the great 
auricular nerve of the cervical plexus, and offsets from it penetrate the sub- 
stance of the gland. 



614 



THE CRANIAL NERVES. 



(a) The buccal branches are directed across the masseter muscle to the angle of 
the mouth ; supplying the muscles, they communicate with the temporo-facial divi- 
sion, and on the buccinator muscle join with filaments of the buccal branch of the 
lower maxillary nerve. 

Fig. 413. 




Fig. 413. SUPERFICIAL DISTRIBUTION OP THE FACIAL, TRIGEMINAL, AND OTHER NKRVES 
OF THE HEAD (from Sappey after Hirschfeld and Leveille). f 

a, References to the Facial Nerve. 1, trunk of the facial nerve after its exit from the 
stylo-mastoid foramen ; 2, posterior auricular branch ; 3, filament of the great auricular 
nerve uniting with the foregoing ; 4, twig to the occipitalis muscle ; 5, twig to the posterior 
auricular muscle ; 6, twig to the superior auricular muscle ; 7, branch to the digastric; 8, 
that to the stylo-hyoid muscle ; 9, superior or temporo-facial division of the pes anseririus ; 
10, temporal branches; 11, frontal ; 12, palpebral or orbital ; 13, nasal or infraorbital ; 
14, buccal ; 15, inferior or cervico-facial division of the nerve ; 16, labial and mental 
branches ; 17, cervical branches. 

by References to the Fifth Nerve. 18, temporo-auricular nerve (of the inferior maxillaiy 
nerve) uniting with tin- facial, giving anterior auricular and parotid branches, and ascend- 
ing to the temporal region ; 19, external frontal or supra-orbital nerve ; 20, internal 
frontal ; 21, palpebral twigs of the lachrymal ; 22, terminal branches of the infra- 
trochlear ; 23, malar twig of the orbito-malar ; 24, external nasal twig of the ethmoidal ; 
25, infraorbital nerve ; 26, buccal nerve uniting with branches of the facial ; 27, labial 
and mental branches of the inferior dental nerve. 

c, Cervical Nerves. 28, great occipital nerve from the second cervical ; 29, great 
auricular nerve from the cervical plexus ; 30, lesser occipital ; 31, another branch with a 
similar distribution ; 32, superficial cervical, uniting by several twigs with the facial. 



AUDITORY NERVE. EIGHTH PAIR. 615 

(b) The supramaxiUary branch, sometimes double, gives an offset over the side of 
the maxilla to the angle of the mouth, and is then directed inwards, beneath the 
depressor of the angle of the mouth, to the muscles and integument between the lip 
and chin ; it joins with the labial branch of the lower dental nerve. 

(c) The inframaxillary branches (r. subcutanei colli), perforate the deep cervical 
fascia, and, placed beneath the platysma muscle, form arches across the side of the 
neck as low as the hyoid bone. Some branches join the superficial cervical nerve 
beneath the platysma, others enter that muscle, and a few perforate it to end in the 
integument. 

Summary. The facial nerve is the motor nerve of the face. It is 
distributed to most of the muscles of the ear, and to the muscles of the 
scalp ; to those of the mouth, nose, and eyelids ; aud to the cutaneous 
muscle of the neck (platysma). It likewise supplies branches to the integu- 
ment of the ear, to that of the side and back of the head, as well as to that 
of the face and the upper part of the neck. 

This nerve is connected freely with the three divisions of the fifth nerve, 
and with the submaxillary and spheno-palatine ganglia ; with the glosso- 
pharyngeal and pneuino-gastric nerves : with the auditory, and with parts 
of the sympathetic and the spinal nerves. 

AUDITORY NERVE. 

The auditory nerve, or portio mollis of the seventh pair, is the special nerve 
of the organ of hearing, and is distributed exclusively to the internal ear. 

As the auditory nerve is inclined outwards from its connection with the 
medulla oblongata to gain the internal auditory meatus, it is in contact 
with the facial nerve, being only separated from it in part by a small artery 
destined for the internal ear. Within the meatus the two nerves are con- 
nected to each other by one or two small filaments. Finally the auditory 
nerve bifurcates in the meatus : one division, piercing the anterior part of 
the cribriform lamina, is distiibuted to the cochlea ; the other, piercing the 
posterior half of the lamina, enters the vestibule of the internal ear. The 
distribution of these branches will be described with the ear. 

EIGHTH PAIR OF NERVES. 

The eighth pair is composed of three distinct nerves the glosso-pharyn- 
geal, pneumo-gastric, and spinal accessory, which leave the skull through the 
anterior and inner division of the foramen lacerum posticum, to the inner 
side and in front of the internal jugular vein. Two of these nerves, the 
glosso-pharyngeal and pneumo-gastric, are attached to the medulla oblongata 
in the same line, and resemble one another somewhat in their distribution, 
for both are distributed to the first part of the alimentary canal. The other, 
the spinal accessory, takes its origin chiefly from the spinal cord, and is 
mainly distributed to muscles ; but it gives fibres to the first two nerves by 
its communicating branch. 

GLOSSO-PHARYNGEAL NERVE. 

The glosso-pharyngeal nerve is destined, as the name implies, for the 
tongue and pharynx. Directed outwards from its place of origin over the 
flocculus to the foramen jngulare, it leaves the skull with the pneumo-gastric 
and spinal- accessory nerves, but in a separate tube of dura mater. In passing 
through the foramen, somewhat in front of the others, this nerve is 
contained in a groove, or in a canal in the lower border of the petrous 



616 



THE CRANIAL NERVES. 



portion of the temporal bone, and presents, successively, two ganglionic 
enlargements, the jugular ganglion, and the petrous ganglion. 

After leaving the skull, the glosso-pharyngeal nerve appears between the 
internal carotid artery and the jugular vein, and is directed downwards over 
the carotid artery and beneath the styloid process and the muscles con- 
nected with it, to the lower border of the stylo-pharyngeus muscle. Here, 
changing its direction, the nerve curves inwards to the tongue, on the 
stylo-pharyngeus and the middle constrictor muscle of the pharynx, above 
the upper laryngeal nerve ; and, passing beneath the hyo-glossus muscle, 
ends in branches for the pharynx, the tonsil, and the tongue. 

Fig. 414. Fig. 414. DIAGRAMMATIC! SKETCH 

PROM BEHIND OF THE ROOTS OF THE 
NERVES OF THE EIGHTH PAIR, WITH 
THEIR GANGLIA AND COMMUNICA- 
TIONS (from Beudz). 

A, part of the cerebellum above the 
fourth ventricle ; B, medulla oMon- 
gata; C, posterior columns of the spinal 
cord ; 1, root of the glosso-pharyngeal 
nerve ; 2, roots of the pneumo-gastric ; 

3, 3, 3, roots of the spinal accessory, 
the uppermost number indicating the 
filaments intermediate between the 
spinal accessory and pneumo-gastric ; 

4, jugular ganglion of the glosso-pha- 
ryngeal ; 5, petrous ganglion ; 6, 
tympanic branch ; 7, ganglion of the 
root of the pneurao-gastric ; 8, auri- 
cular branch ; 9, long ganglion on the 
trunk of the pneumo-gastric; 10, 
branch from the upper ganglion to the 
petrous ganglion of the glosso-pharyn- 
geal ; 11, inner portion of the spinal 
accessory ; 12, outer portion ; 13, 
pharyngeal branch of the pneumo- 
gastric ; 14, superior laryngeal 

branch ; 15, twigs connected with the sympathetic ; 16, fasciculus of the spinal accessory 
prolonged with the pneumo-gastric. 

The jugular ganglion, the smaller of the two ganglia of the glosso- 
pharyngeal nerve, is situated at the upper part of the osseous groove in 
which the nerve is laid during its passage through the jugular foramen. 
Its length is from half a line to a line, and the breadth from half to three 
fourths of a line. It is placed on the outer side of the trunk of the nerve, 
and involves only a part of the fibres, a small fasciculus passing over the 
ganglion, and joining the nerve below it. 

The petrous ganglion is contained in a hollow in the lower border of the 
petrous part of the temporal bone (receptaculuin ganglioli petrosi), and 
measures about three lines in length. This ganglion includes all the fila- 
ments of the nerve, and resembles the gangliform enlargement of the facial 
nerve. From, it arise the small branches by which the glosso-pharyngeal is 
connected with other nerves at the base of the skull : these are the tympanic 
nerve, and the branches which join the pneumo-gastric and sympathetic. 

CONNECTING BEANCHES, AND TYMPANIC BRANCH. 

From the petrous ganglion spring three small connecting filaments. One passes 
to the auricular branch of the pneumo-gastric, one to the upper ganglion of the sym- 




GLOSSO-PHARYXGEAL NERVE. 



617 



pathetic or vice versd, and a third to the ganglion of the root of the pneumo -gastric 
nerve. The last is not constant. 

There is sometimes likewise a filament from the digastric branch of the facial nerve, 
which, piercing the digastric muscle, joins the glosso-pharyngeal nerve below the 
petrous ganglion. 

The tympanic branch (nerve of Jacobson), arises from the petrous ganglion, and is 
conducted to the tympanum by a special canal, the orifice of which is in the ridge of 
bone between the jugular fossa and the carotid foramen. On the inner wall of the 
tympanum the nerve joins with a twig from the sympathetic in a plexus (tym- 
panic), and distributes filaments to the membrane lining the tympanum and the 
Eustachian tube, as well as one to the fenestra rotunda, and another to the fenestra 
ovalis. 



Fig. 415 



Fig. 415. SKETCH OP THE TYMPANIC 
BRANCH OF THE GLOSSO-PHARYN- 
GEAL NERVE, AND ITS CONNECTIONS 
(from Breschet). 

A, squamous part of the left tem- 
poral bone ; B, petrous part ; C, in- 
ferior maxillary nerve ; D, internal 
carotid artery ; a, tensor tympani 
muscle ; 1, carotid plexus ; 2, otic 
ganglion ; 3, glosso-pharyngeal nerve ; 
4, tympanic nerve ; 5, twigs to the 
carotid plexus ; 6, twig to fenestra 
rotunda ; 7, twig to fenestra ovalis ; 
8, junction with the large superficial 
petrosal nerve ; 9, small superficial 
petrosal ; 10, twig to the tensor tym- 
pani muscle; 11, facial nerve; 12, 
chorda tyrapani ; 13, petrous ganglion 
of the glosso-pharyngeal ; 14, twig to 
the membrane of the Eustachian tube. 



From the tympanic nerve are 
given three connecting branches, 
by which it communicates with 
other nerves; and which occupy 
channels given off from the osseous 

canal through which the nerve enters the tympanum. One branch enters the carotid 
canal and joins with the (sympathetic on the carotid artery. A second is united to 
the large superficial petrosal nerve, as this lies in the hiatus Fallopii. And the 
third is directed upwards, beneath the canal for the tensor tympani muscle, towards 
the surface of the petrous portion of the temporal bone, where it becomes the small 
petrosal nerve; and under this name it is continued to the exterior of the skull 
through a small aperture in the sphenoid and temporal bones, to end in the otic 
ganglion. As this petrosal nerve passes the gangliform enlargement of the facial, it 
has a connecting filament with that enlargement, which is by some considered its 
principal posterior termination. 

Jacobson described an anterior or internal branch from the tympanic nerve to the 
spheno-palatine ganglion. 




BRANCHES DISTRIBUTED IN THE NECK. 

The carotid branches course along the internal carotid artery, and unite with the 
pharyngeal branch of the pneumo-gastric, and with branches of the sympathetic. 

The pharyngeal branches, three or four in number, unite opposite the middle con- 
strictor of the pharynx with branches of the pneumo-gastric and sympathetic to form 
the pharyngeal plexus. Nerves to the mucous membrane of the pharynx perforate 
the muscles, and extend upwards to the base of the tongue and the epiglottis, and 
downwards nearly to the hyoid bone. 



618 THE CRANIAL NERVES. 

The muscular branches are given to the stylo-pharyngeus and constrictor 
muscles. 

Tonsilitic brandies. When the glosso-pharyngeal nerve is near the tonsil, some 
branches are distributed on that body in a kind of plexus (circulus tonsillaris). From 
these nerves offsets are sent to the soft palate and the isthmus of the fauces. 

Lingual branches. The glosso-pharyngeal nerve divides into two parts at the 
border of the tongue. One turns to the upper surface of the tongue, supplying the 
mucous membrane at its base ; the other perforates the muscular structure, and ends 
in the mucous membrane on the lateral part of the tongue. Some filaments enter 
the circumvallate papillae. 

Summary. The glosso-pharyngeal nerve distributes branches to the 
mucous membrane of the tongue, pharynx, tympanum, and Eustachian tube. 
The muscles supplied by it are some of those of the pharynx and base of the 
tongue. It is connected with the following nerves, viz., the lower maxillary 
division of the fifth, the facial, the pneumo-gastric (the trunk and branches 
of this nerve), and the sympathetic. 



PNEUMO-GASTRIC NERVE. 

The pneumo-gastric nerve (nervus vagus, par vagum) has the longest 
course of any of the cranial nerves. It extends through the neck and the 
cavity of the chest to the upper part of the abdomen ; and it supplies nerves 
to the organs of voice and respiration, to the alimentary canal as far as the 
stomach, and to the heart. 

The filaments by which this nerve springs from the medulla oblongata 
are arranged in a flat fasciculus, immediately beneath the glosso-pharyngeal 
nerve, and directed outwards with that nerve, across the flocculus to the 
jugular foramen. 

In passing through the opening at the base of the skull the pneumo- 
gastric nerve is contained in the same sheath of dura mater, and surrounded 
by the same tube of arachnoid membrane as the spinal-accessory nerve ; but 
it is separated from the glosso-pharyngeal nerve by a process of membrane. 
In the foramen the filaments of the nerve become aggregated together ; and 
it here presents a ganglionic enlargement, distinguished as the ganglion of 
the root of the pneumo-gastric. After its passage through the foramen, it 
is joined by the accessory part of the spinal accessory nerve, and a second 
ganglion is formed upon it, the ganglion of the trunk of the nerve. Several 
communications are at the same time established with the surrounding 
nerves. 

The upper ganglion, or ganglion of the root of the pneumo-gastric nerve, 
situated in the foramen jugulare, is of a greyish colour, nearly spherical, and 
about two lines in diameter ; it has filaments connecting it with other nerve*, 
viz., with the facial, the petrous ganglion of the glosso-pharyngeal, the 
spinal accessory, and the sympathetic. 

The lower ganglion, or ganglion of the trunk or the pneumo-gastric nerve, 
is about half an inch below the preceding. Occupying the trunk of the 
nerve outside the skull, it is of a flattened cylindrical form and reddish 
colour, and measures about ten lines in length and two in breadth. The 
ganglion does not include all the fibres of the nerve; the fasciculus, which 
is sent from the spinal accessory to join the vagus, is the part not in- 
volved in the ganglionic substance. It communicates with the hypoglossal, 
the spinal, and the sympathetic nerves. 

The pneumo-gastric nerve descends in the neck, between and concealed 



PXEUMO-GASTRIC NERVE. 



619 



by the internal jugular vein and the internal carotid artery, and afterwards 
similarly between that vein and the common carotid artery, being enclosed 
along with them in the sheath of the vessels. As they enter the thorax, 
the nerves of the right and left side present some points of difference. 

Fig 416. DIAGRAM OF THE ROOTS Fig. 416. 

AND ANASTOMOSING BRANCHES OF 
THE NERVES OF THE EIGHTH PAIR 
AND NEIGHBOURING NERVES (from 
Sappey after Hirschfeld and Le- 
veille). 

1, facial nerve ; 2, glosso-pharyn- 
geal with the petrous ganglion repre- 
sented ; 2', connection of the digastric 
branch of the facial neive with the 
glosso-pharyngeal nerve ; 3, pneu- 
mo-gastric, with both its ganglia re- 
presented ; 4, spinal access ry ; 5, 
hypoglossal ; 6, superior cervical 
ganglion of the sympathetic ; 7, loop of 
union between the two first cervical 
nerves ; 8, carotid branch of the sym- 
pathetic ; 9, nerve of Jacobson (tym- 
panic), given off from the petrous 
ganglion ; 10, its filaments to the 
sympathetic; 11, twig to the Eusta- 
chian tube ; 12, twig to the fenestra 
ovalis; 13, twig to the fenestra ro- 
tun'la ; 14, twig of union with the 
small superficial petrosal ; 15, twig of 
union with the large superficial petro- 
s tl ; 16, otic ganglion ; 17, branch of 
the jugular fossa, giving a filament to 
the petrous ganglion ; 18, union 
of the spinal accessory with the pneu- 
mo-gastric ; 19, union of the hypo- 
glossal with the first cervical nerve ; 
20, union between the sterno-mastoid 
branch of the spinal accessory and 
that of the second cervical nerve ; 21, 

pharyngeal plexus ; 22, superior laryngeal nerve ; 23, external laryngeal ; 24, middle 
cervical ganglion of the sympathetic. 

On the rirjht side the nerve crosses over the first part of the right sub- 
clavian artery, at the root of the neck, and its recurrent laryngeal branch 
turns backwards and upwards round that vessel. The n rve then enters 
the thorax behind the right innominate vein, and descends on the side of the 
trachea to the back of the root of the lung, where it spreads out in the pos- 
terior pulmonary plexus. It emerges from this plexus in the form of two 
cords, which are directed to the resophagus. and uniting and subdividing 
form, with similar branches of the nerve of the left side, the oesophageal 
plexus. Near the lower part of the oesophagus the branches, which have 
thus interchanged fibres with the nerve of the left side, are gathered 
again into a single trunk, which, descending on the back of the oesophagus, 
is spread out on the posterior or inferior surface of the stomach. 

On the left side the pueumo-gastric nerve, entering the thorax between 
the left carotid and subclavian arteries and behind the left innominate vein, 
lies further forwards than the right nerve, and crosses over the arch of the 
aorta, while its recurrent laryngeal branch turns up behind the arch. It 

s s 2 




620 



THE CRANIAL NERVES. 



then passes behind the root of the left lung, and, emerging from the 
posterior pulmonary plexus, is distributed like its fellow to the oesophagus. 

Fig. 417. 




Fig. 417. VIEW OP THE NERVES OP THE EIGHTH PAIR, THEIR DISTRIBUTION AND 
CONNECTIONS ON THE LEFT SIDE (from Sappey after Hirschfeld and Leveilld). 3 

1, pneumo-gastric nerve in the neck ; 2, ganglion of its trunk ; 3, its union with the 
spinal accessory ; 4, its union with the hypoglossal ; 5, pharyngeal branch ; 6, superior 
laryngeal nerve ; 7, external laryngeal ; 8, laryngeal plexus ; 9, inferior or recur- 
rent laryngeal ; 10, superior cardiac branch; 11, middle cardiac; 12, plexiform part 
of the nerve in the thorax; 13, posterior pulmonary plexus ; 14, lingual or gustatory 
nerve of the inferior maxillary ; 15, hypoglossal, passing into the muscles of the tongue, 
giving its thyro-hyoid branch, and uniting with twigs of the lingual ; 16, glosso-pharyngeal 
nerve; 17, spinal accessory nerve, uniting by its inner branch with the pneumo-gastric, 
and by its outer, passing into the sterno-mastoid muscle ; 18, second cervical nerve ; 19, 
third; 20, fourth; 21, origin of the phrenic nerve; 22, 23, fifth, sixth, seventh, and 
eighth cervical nerves, forming with the first dorsal the brachial plexus ; 24, superior 
cervical ganglion of the sympathetic ; 25, middle cervical ganglion ; 26, inferior cervical 
ganglion united with the first dorsal ganglion; 27, 28, 29, 30, second, third, fourth, and 
fifth dorsal ganglia. 



PNEUMO-GASTR1C XERVE. 621 

Inferiorly, it forms a single trunk in front of the oesophagus, and is spread 
out on the anterior or superior surface of the stomach. 

There are various circumstances in the distribution of the pneumo-gastric nerves 
which at first sight appear anomalous, but which are explained by reference 
to the process of development. The recurrent direction of the inferior laryngeal 
branches in all probability arises from the extreme shortness or rather absence of the 
neck in the embryo at first, and from the branchial arterial arches having originally 
occupied a position at a higher level than the parts in which those branches are 
ultimately distributed, and having dragged them down as it were in the descent of 
the heart from the neck to the thorax. The recurrent direction may therefore be 
accepted as evidence of the development of those nerves before the occurrence of 
that descent. The circumstance that one recurrent laryngeal nerve passes round the 
subclavian artery, and the other round the aorta, is seen to arise from an originally 
symmetrical disposition, when it is remembered that the innominate artery and the 
arch of the aorta are derived from corresponding arches of the right and left sides. 
The supply of the back of the stomach by the right pneumo-gastric nerve, and of the 
front by the left nerve, is connected with the originally symmetrical condition of the 
alimentary canal, and the turning over of the stomach on its right side in its sub- 
sequent growth. 

BRANCHES OF THE PNEUMO-GASTRIC NERVE. 

Some of its branches serve to connect the pneumo-gastric with other 
nerves, and others are distributed to the muscular substance or the mucous 
lining of the organs which the nerve supplies. The principal con- 
necting branches of this nerve are derived from the ganglia. In the 
different stages of its course branches are supplied to various organs aa 
follows. In the jugular foramen, a branch is given to the ear ; in the neck, 
branches are furnished successively to the pharynx, the larynx, and the 
heart ; and in the thorax, additional branches are distributed to the heart, 
as well as to the lungs and the oesophagus. Terminal branches in the 
abdomen are distributed to the stomach, liver, and other organs. 

CONNECTING BRANCHES AND AURICULAR BRANCH. 

Connections between the upper ganglion of the vagus nerve and the spinal accessory, 
glosso-pharyngeal, and sympathetic nerves. The connection with the spinal accessory 
is effected by one or two filaments. The filament to the petrous ganglion of the 
glosso-pharyngeal is directed transversely ; it is not always present. The communi- 
cation with the sympathetic is established by means of the ascending branch of the 
upper cervical ganglion. 

The auricular branch is continued to the outer ear. Arising from the ganglion of 
the root, this branch is joined by a filament from the glosso-pharyngeal nerve, and 
then turns backwards along the outer boundary of the jugular foramen to an opening 
near the styloid process. Next, it traverses the substance of the temporal bone, 
crossing the aqueduct of Fallopius, about two lines from the lower end, and, reaching 
the surface between the mastoid process and the external auditory meatus, is distri- 
buted to the integument of the back of the ear. On the surface it joins with a twig 
from the posterior auricular branch of the facial nerve. 

Connections of the second ganglion with the hypoglossal, sympathetic, and spinal 
nerves. This ganglion is connected by filaments with the trunk of the hypoglossal, 
with the upper cervical ganglion of the sympathetic, and with the loop formed between 
the first two cervical nerves. 

PHARYNGEAL BRANCH. 

The pharyngeal branch arises from the upper part of the ganglion of the 
trunk of the nerve. In its progress inwards to the pharynx this nerve 
crosses in some cases over, in others under the internal carotid artery ; and 



622 THE CRANIAL NERVES. 

it divides into branches, which, conjointly with others derived from the 
glosso-pharyngeal, the superior laryngeal, and the sympathetic nerves, form 
a plexus (pharyngeal) behind the middle constrictor of the pharynx. From 
the plexus branches are given to the muscular structure, and to the mucous 
membrane of the pharynx. As the pharyngeal nerve crosses the carotid 
artery, it joins filaments which the glosso-pharyngeal distributes on the same 
vessel. There is sometimes a second pharyngeal branch. 

SUPERIOR PHARYNGEAL BRANCH. 

This nerve springs from the middle of the ganglion of the trunk of the 
pneumo-gastric nerve. It is directed inwards to the larynx beneath the 
internal carotid artery, and divides beneath that vessel into two branches, 
distinguished as external and internal laryngeal, both of which ramify in 
the structures of the larynx. 

The external laryngeal branch, the smaller of the two divisions, gives 
backwards, at the side of the pharynx, filaments to the pharyugeal plexus 
and the lower constrictor muscle ; and it is finally prolonged beneath the 
muscles on the side of the larynx to the crico thyroid muscle in which it 
ends. In the neck this branch joins the upper cardiac nerve of the 
sympathetic. 

The internal laryngeal branch is continued to the interval between the 
hyoid bone and the thyroid cartilage, where it perforates the thyro-hyoid 
membrane with the laryngeal branch of the superior thyroid artery, and dis- 
tributes filaments to the mucous membrane : some of these are directed up- 
wards in the aryteno-epiglottidean fold of mucous membrane to the base of the 
tongue, the epiglottis, and the epiglottidean glands; while others are reflected 
downwards in the lining membrane of the larnyx, extending to the corda 
vocalis, on the inner side of the laryngeal pouch. A slender communicating 
branch to the recurrent laryngeal nerve descends beneath the lateral part of 
the thyroid cartilage. A branch enters the arytenoid muscle, some fila- 
ments of which seem to end in the muscle, while others proceed through 
it to the mucous membrane. 



RECURRENT LARYNGEAL BRANCH. 

The recurrent or inferior laryngeal branch of the vagus nerve, as the 
name expresses, has a reflex course to the larnyx. 

The nerve on the right side arises at the top of the thorax, winds round 
the subclavian artery, and passes beneath the common carotid and inferior 
thyroid arteries in its course towards the trachea. On the left side the re- 
current nerve is bent round, below and behind the arch of the aorta, imme- 
diately beyond the point where the obliterated ductus arteriosus is con- 
nected with the arch, and is thence continued upwards to the trachea. 

Each nerve in its course to the larynx is placed between the trachea and 
oesophagus, supplying branches to both tubes ; and each, while making its 
turn round the artery, gives nerves to the deep cardiac plexus. At the 
lower part of the cricoid cartilage the recurrent nerve distributes branches 
to supply all the special muscles of the larynx, except the crico-thyroid 
muscle, which is supplied from the upper laryngeal nerve. It likewise 
gives a few offsets to the mucous membrane, and a single communicating 
filament which joins the long branch of the upper laryngeal nerve beneath 
the side of the thyroid cartilage. 



BRANCHES OF PNEUMO-GASTRIC NERVE. 623 

CARDIAC BRANCHES. 

Branches to the heart are given off by the pneumo-gastric nerve both in 
the neck and in the thorax. 

The cervical cardiac branches arise at both the upper and the lower part 
of the neck. The upper branches are small, and join the cardiac nerves of 
the sympathetic. The loiver, a single branch, arises as the pneumo-gastric 
nerve is about to enter the chest. On the right side this branch lies by the 
side of the innominate artery, and joins one of the cardiac nerves destined 
for the deep cardiac plexus ; it gives some filaments to the coats of the 
aorta. The branch of the left side crosses the arch of the aorta, and ends 
in the superficial cardiac plexus. 

The thoracic cardiac branches of the right side leave the trunk of the 
pneumo-gastric as this nerve lies by the side of the trachea, and some 
are also derived from the first part of the recurrent branch : they pass 
inwards on the air- tube, and end in the deep cardiac plexus. The 
corresponding branches of the left side come from the left recurrent 
laryngeal nerve. 

PULMONARY BRANCHES. 

Two sets of pulmonary branches are distributed from the pneumo-gastric 
nerve to the lung ; and they reach the root of the lung, one on its fore part, 
the other on its posterior aspect. The anterior pulmonary nerves, two or 
three in number, are of small size. They join with filaments of the 
sympathetic ramified on the pulmonary artery, and with these nerves 
constitute the anterior pulmonary plexus. Behind the root of the lung the 
pneumo-gastric nerve becomes flattened, and gives several branches of much 
larger size than the anterior branches, which, with filaments derived from 
the second, third, and fourth thoracic ganglia of the sympathetic, form the 
posterior pulmonary plexus. Offsets from this plexus extend along the rami- 
fications of the air-tube through the substance of the lung. 

CESOPHAGEAL BRANCHES. 

The oesophagus within the thorax receives branches from the pneumo- 
gastric nerves, both above and below the pulmonary branches. The lower 
branches are the larger, and are derived from the cesophageal plexus, formed 
by connecting cords between the nerves of the right and left sides, while 
they lie in contact with the oesophagus. 

GASTRIC BRANCHES. 

The branches distributed to the stomach (gastric nerves) are the terminal 
branches of bath pneumo-gastric nerves. The nerve of the left side, on 
arriving in front of the oesophagus, opposite the cardiac orifice of the 
stomach, divides into many branches : the largest of these extend over the fore 
part of the stomach ; others lie along its small curvature, and unite with 
branches of the right nerve and the sympathetic ; and some filaments are 
continued between the layers of the small omentum to the hepatic plexus. 
The right pneumo-gastric nerve descends to the stomach on the back of the 
gullet and distributes branches to the posterior surface of the organ : a part 
of this nerve is continued from the stomach to the left side of the coeliac 
plexus, and to the splenic plexus of the sympathetic. 

Summary. The pneumo-gastric nerves supply branches to the upper part 
of the alimentary canal, viz., the pharynx, oesophagus, and stomach with 
the liver and spleen ; and t6 the respiratory passages, namely, the larynx, 



Fig. 418. 



40 23 24 26 . 



PXEUMO-GASTRIC.-SPINAL ACCESSORY NERVE. 625 

Fig. 418. VIEW OF THE DISTRIBUTION AND CONNECTIONS OP THE PNEUMO-GASTRIO AND 
SYMPATHETIC NERVES ON THE RIGHT SIDE (from Hirschfeld and Leveille). f 

a, lachrymal gland ; b, sublingual gland ; c, submaxillary gland and facial artery ; 
d, thyroid gland, pulled forwards by a hook ; e, trachea, below which is the right 
bronchus cut across; /, the gullet; g, the stomach, divided near the pylorus ; i, trans- 
verse colon, with some folds of intestine below. 

A, heart, slightly turned aside to show the cardiac plexus, &c. ; B, aortic arch, drawn 
forward by a hook ; C, innominate artery ; D, subclavian artery, of which a portion has 
been removed to show the sympathetic ganglia ; E, inferior thyroid artery ; F, a divided 
part of the external carotid artery, upon which runs a nervous plexus ; Q-, internal 
carotid, emerging from its canal superiorly; H, thoracic aorta; K, intercostal vein; L, 
pulmonary trunk, the right branch cut ; M, superior vena cava ; 0, intercostal artery. 

1, ciliary nerves of the eyeball ; 2, branch of the oculo-motor to the inferior oblique 
muscle, connected with the ophthalmic ganglion ; 3, 3, 3, the three principal divisions of 
the trifacial nerve ; 4, ophthalmic ganglion ; 5, spheno-palatine ; 6. otic ; 7, submaxillary ; 
8, sublingual ; 9, sixth nerve ; 10, facial in its canal, uniting with the spheno-palatine 
and otic ganglia; 11, glosso-pharyngeal; 12, right pneumo-gastric ; 13, left pneumo- 
gastric spreading on the anterior surface of the stomach ; 14, spinal accessory ; 35, hypo- 
glossal ; 16, lower nerve of the cervical plexus; 17, middle nerve of the brachial 
plexus ; 18, intercostal nerves ; 21, superior cervical ganglion of the sympathetic, con- 
nected with, 22, tympanic nerve of Jacobson ; 23, carotid branch of the Vidian nerve ; 
24, cavernous plexus; 25, ophthalmic twig; 26, filament to the pituitary gland; 27, 
union with the upper cervical nerves ; 28, points to the pneurao-gastric nerve, close to 
the pharyngeal and carotid branches : 29, points to the superior laryngeal nerve, close 
to the pharyngeal and inter-carotid plexuses ; 30, laryngeal branch joining the laryngeal 
plexus ; 31, great sympathetic nerve ; 32, superior cardiac nerve ; 33, middle cervical 
ganglion ; 34, twig connecting the ganglion with, 35, the recurrent ; 36, middle cardiac 
nerve ; 37, great sympathetic nerve ; 38, inferior cervical ganglion ; below 37, branches 
from the ganglion, passing round the subclavian and vertebral arteries ; 39, the line from 
this number crosses the nerves proceeding from the brachial plexus ; 40, sympathetic 
twigs surrounding the axillary artery ; 41, branch of union with the first intercostal 
nerve ; the line from the letter e, pointing to the trachea, crosses the superior, middle, 
and inferior cardiac nerves ; 42, cardiac plexus and ganglion ; 43, 44, right aud left coro- 
nary plexuses ; 45, 46, thoracic portion of the great sympathetic nerve and ganglia, showing 
their connections with the intercostal nerves ; 47, great splanchnic nerve; 48, semilunar 
ganglion ; 49, lesser splanchnic ; 50, solar plexus ; 51, union with the pneumo-gastric 
nerve ; 52, diaphragmatic plexus and ganglion ; 53, coronary plexus ; 54, hepatic ; 55, 
splenic ; 56, superior mesenteric ; 57, renal plexus. 

trachea, and its divisions in the lungs. These nerves give branches likewise 
to the heart and great vessels by means of their communication with the 
cardiac plexus. Each pneumo-gastric nerve is connected with the following 
cranial nerves the spinal accessory, glosso-pharyngeal, facial, and hypo- 
glossal ; also, with some spinal nerves ; and with the sympathetic in the 
neck, thorax, and abdomen. 

SPINAL ACCESSORY NERVE. 

The spinal nerve accessory to the vagus, or, as it is shortly named, the 
spinal accessory nerve, consists of two parts : one (accessory) joins the 
trunk of the pneumo-gastric ; the other (spinal) ends in branches to the 
stern o-mastoid and trapezius muscles. 

The internal or accessory part, the smaller of the two, joins in the foramen 
of exit the ganglion on the root of the pneumo-gastric, by two or three 
filaments ; and having passed from the skull, blends with the trunk of the 
pneumo-gastric beyond its second ganglion, as already said. 

It is stated by Bendz that a filament is given from the spinal accessory to the pha- 
ryngeal nerve above the place of junction with the pneumo-gastric, and that fibrils of 
the same nerve have been traced into each of the muscular offsets of the pneumo- 
gastric nerve. (Bendz, " Tract, de connexu inter nerv. vag. et acces." 1836.) 

The external portion of the nerve communicates with the accessory part 



626 THE CRANIAL NERVES. 

in the foramen j ugulare. After issuing from the foramen, the nerve is directed 
backwards across the internal jugular vein, in some cases over, in others under 
it, and perforates the sterno-mastoid muscle, supplying this with branches, 
and joining amongst the fleshy fibres with branches of the cervical plexus. 
Descending in the next place across the neck behind the sterno-mastoid, the 
nerve passes beneath the trapezius muscle. Here it forms a kind of plexus 
with branches of the third and fourth cervical nerves, and distributes fila- 
ments to the trapezius, which extend nearly to the lower edge of the muscle. 

NINTH PAIR OF NERVES. 

The hypoglossal or ninth cranial nerve is the motor nerve of the tongue, 
and in part of some muscles of the neck. 

The filaments by which this nerve arises from the medulla oblongata are 
collected into two bundles, which converge to the anterior condyloid 
foramen of the occipital bone. Each bundle of filaments perforates the 
dura mater separately within the foramen, and the two are joined after 
they have passed through it. 

After leaving the cranium, this nerve descends almost vertically to the 
lower border of the digastric muscle, whera, changing its course, it is 
directed forwards above the hyoid bone to the under part of the tongue, 
It lies at first very deeply with the vagus nerve, to which it is connected ; 
but passing between the internal carotid artery and the jugular vein, it 
curves forward round the occipital artery, and then crosses over the external 
carotid below the digastric muscle. Above the hyoid bone it is crossed by 
the lower part of the stylo-hyoid muscle and posterior belly of the digastric, 
and rests on the hyo-glossus muscle. At the anterior border of the hyo- 
glossus it is connected with the gustatory nerve, and is continued in the 
fibres of the genio-hyo-glossus muscle beneath the tongue to the tip, 
distributing branches upwards to the muscular substance. 

The principal branches of this nerve are distributed to the muscles 
ascending to the larynx and hyoid bone, and to those of the tongue ; a few 
serve to connect it with some of the neighbouring nerves. 

In animals the ninth nerve not unfrequently possesses a posterior root furnished with 
a ganglion, in the same manner as that of a spinal nerve. 

CONNECTING BRANCHES. 

Connection with the pneumo-gastric. Close to the skull the hypoglossal nerve is 
connected with the second ganglion of the pneumo-gastric by separate filaments, or 
in some instances the two nerves are united so as to form one mass. 

Union with the sympathetic and first two spinal nerves. Opposite the first cervical 
vertebra the nerve communicates by several twigs with the upper cervical ganglion 
of the sympathetic, and with the loop uniting the first two spinal nerves in front of 
the atlas. 

MUSCULAR AND LINGUAL BRANCHES. 

Descending branch of the ninth nerve. This branch (r. descendens noni), 
leaves the ninth nerve where this turns round the occipital artery, or, some- 
times, higher up. It passes downwards on the surface of the sheath of 
the carotid vessels, gradually crossing from the outer to the inner side, 
gives a branch to the anterior belly of the omo hyoid muscle, and joins 
about the middle of the neck in a loop with one or two branches from 
the second and third cervical nerves, forming the ansa hypoylossi. The 
concavity of this loop is turned upwards ; and the connection between 
the nerves is effected by means of two or more interlacing filaments, which 



HYPOGLOSSAL NERVE. 



627 



enclose an irregularly shiped space. From this interlacement of the nerves, 
filaments are continued backwards to the posterior belly of the omo-hyoid, 
and downwards to the sterno-hyoid and stern o- thyroid muscles. Occasionally 
a filament is continued to the chest, where it joins the cardiac and phrenic 
nerves. 

Fig 419 







Fig. 419. VIEW OF THE DISTRIBUTION OP THK SPINAL ACCESSORY AND HrpoaiossAi, 
NERVES (from Sappey after Hirschfeld and Leveille). ^ 

1, lingual nerve ; 2, pneumo-gasiric nerve ; 3, superior laryngeal (represented too large) ; 
4, external laryngeal branch ; 5, spinal accessory ; 6, second cervical ; 7, third ; 8, 
fourth ; 9, origin of the phrenic nerve; 10, origin of the branch to the subclavius muscle ; 
11, anterior thoracic nerves ; 12, hypoglossal nerve ; 13, its descending branch ; 14, com- 
municating branch from the cervical nerves; 15, 16, 18, 19, descending branches from 
the plexiform union of these nerves to the sterno-hyoid, sterno-thyroid, and omo-hyoid 
muscles ; 17, branch from the descendens noni to the upper belly of the omo-hyoid 
muscle ; 20, branch from the hypoglossal nerve to the tbyro-hyoid muscle ; 21, communi- 
cating twigs from the hypoglossal to the lingual nerve ; 22, terminal distribution of the 
hypoglossal to the muscles of the tongue. 

It is not uncommon to find the descending branch of the ninth nerve within the 
sheath of the large cervical vessels, and in such cases it is placed either over or under 
the vein. This nerve in some cases appears to be derived either altogether from the 
pneumo-gastric, or from both the pneumo-gastric and hypoglossal nerves. There is 
every reason, however, to believe that these varieties in origin are only apparent, 
arising from the temporary adhesion of the filaments of this branch to those of the 



628 THE CRANIAL NERVES. 

pneumo-gastric. It is probable, moreover, that the descendens noni has little if any 
real origin from the hypoglossal nerve : Luschka states it as the result of numerous 
researches on the human subject that the descendens noni usually contains no fila- 
ments from the hypoglossal, but is a branch from the first and second cervical, tem- 
porarily associated with the ninth nerve ; and this quite agrees with the circumstance 
that in the domestic animals the branches supplied to those muscles to which the 
descendens noni of the human subject is distributed come from the cervical plexus. 

Branches to muscles and the tongue. The branch to the thyro-hyoid 
muscle is a separate twig given off from the hypoglossal nerve as it 
approaches the hyoid bone. The nerve supplies branches to the stylo -hyoid, 
hyo-glossus, genio-byoid, and genio-hyo-gloasus muscles as it becomes 
contiguous to each, and, when arrived close to the middle of the tongue 
with the ranine artery, gives off several long slender branches, which pass 
upwards into the substance of the organ. Some filaments join with others 
proceeding from the gustatory nerve. 

A branch is described as uniting with its fellow of the opposite side, in the sub- 
stance of the genio-hyoid muscle, or between it and the genio-glossus. This loop, as 
also the ansa hypoglossi, is recommended by Hyrtl as a particularly favourable 
example for the observation of nerve-fibres returning to the nervous centres without 
distribution, to which he gives the name of " nerves without ends." (" Nat. Hist. 
Review," Jan. 1862.) That in the ansa hypoglossi an interchange of fibres takes 
place, so that a filament of the spinal nerve is directed upwards along the branch of 
the hypoglossal, and vice versa, was noticed by Cruveilhier. 

Summary. The hypoglossal nerve supplies, either alone or in union 
with branches of the spinal nerves, all the muscles connected with the 
os hyoides, including those of the tongue, with the exception of the digastric 
and stylo-hyoid, the mylo-hyoid, and the middle constrictor of the pharynx. 
It also supplies the sterno -thyroid muscle. 

It is connected with the following nerves, viz., pneumo-gastrie, gustatory, 
three upper cervical nerves, and the sympathetic. 



B. SPINAL NERVES. 

The spinal nerves are characterised by their origin from the spinal cord, 
and their direct transmission outwards from the spinal canal in the intervals 
between the vertebrae. Taken together, these nerves consist of thirty-one 
pairs ; and, according to the region in which they issue from the spinal 
canal, they are named cervical, dorsal, lumbar, sacral, and coccygeal. 

By universal usage each pair of nerves in the dorsal, lumbar, and sacral 
regions is named in correspondence with the vertebra beneath which it 
emerges. There are thus left eight pairs of nerves between the cranium 
and the first dorsal nerve, the first being placed above the atlas and the 
eighth below the seventh cervical vertebra, which are reckoned by the 
majority of writers as eight cervical nerves. The nerves of the thirty-first 
pair emerge from the lower end of the sacral canal, below the first vertebra 
of the coccyx, and are named coccygeal. 

Although the plan of counting eight cervical nerves is continued in this work for 
the sake of convenience, it being that which is most frequently followed, it is by no 
means intended to represent this method as scientifically correct. The plan of 
\Villis, who reckoned the suboccipital as a cranial nerve, had at least the advantage 
that it made the numbers of the remaining seven cervical nerves correspond each 
with the vertebra beneath which it emerged, as do the dorsal, lumbar and sacral 
nerves; and if the suboccipital nerve, while recognised as the first spinal nerve, be 



TEE SPINAL NERVES. ROOTS. 



kept distinct from the seven which succeed, 
as is taught in some schools, a nomenclature 
is arrived at much less objectionable than that 
which is most prevalent. A reference, however, 
to development (p. 17) will remind the reader 
that in the primordial vertebrae each spinal 
nerve is originally situated above the rib and 
transverse process belonging to the same seg- 
ment; and it will become apparent that the 
scientifically accurate nomenclature of nerves 
might be rather to name each in accordance 
with the number of the vertebra below it. Thus 
the eighth cervical nerve would be called first 
dorsal, and so on. 

Fig. 420. DIAGRAMMATIC OUTLINE OF THE ROOTS 
AND FIRST PART OF THE SPINAL NERVES, 
TOGETHER WI1H THE SYMPATHETIC CORD OF 

ONE SIDE. ^ 

The view is taken from before. In the upper 
part of the figure the pons Varolii and medulla 
oblongata are represented, and from V, to IX, 
the roots of the several cranial nerves from the 
trifacial to the hypoglossal are indicated. On 
the left side C 1, is placed opposite the first cer- 
vical or suboccipital nerve ; and the numbers 2 to 
8 following below indicate the corresponding cer- 
vical nerves; Br, indicates the brachial plexus ; 
D 1, is placed opposite the intercostal part of the 
first dorsal nerve, and the numbers 2 to 12 follow- 
ing mark the corresponding dorsal nerves ; S 1, 
the first lumbar nerve, and the numbers 2 to 5 
following the remaining lumbar nerves; Cr, the 
anterior crural, and o, the obturator nerve ; SI, 
the first sacral, and the following numbers 2 to 5, 
the remaining sacral nerves ; 6, the coccygeal 
nerve; Sc, the great sciatic nerve; +, +, the 
filum terrainale of the cord. 

On the right side of the figure the following 
letters indicate parts of the sympathetic nerves ; 
viz., a, the superior cervical ganglion, com- 
municating with the upper cervical spinal nerves 
and continued below in the great sympathetic 
cord ; b, the middle cervical ganglion ; c, d, the 
lower cervical ganglion united with the first 
dorsal ; d', the eleventh dorsal ganglion ; from 
the fifth to the ninth dorsal ganglia the origins 
of the great splanchnic nerve are shown ; I, the 
lowest dorsal or upper lumbar ganglion ; ss, the 
upper sacral ganglion. In the whole extent of the 
sympathetic cord, the twigs of union with the 
spinal nerves are shown. 



Br 



Sometimes an additional coccygeal nerve 
exists. Among seven cases which appear to 
have been examined with great care, Professor 
Schlemm (" Observat. Neurolagicee,'' Berolini, 
1834) found two coccygeal nerves on each side 
in one instance, and on one side in another 
case. In all the rest there was only a single 
coccygeal nerve on each side. 



Icr 



Sc 



630 



THE SPINAL NERVES. 



THE ROOTS OF THE SPINAL NERVES. 

Each spinal nerve springs from the spinal cord by two roots which 
approach one another, and, as they quit the spinal canal, join in the 
corresponding intervertebral foramen into a single cord ; and each cord so 
formed separates immediately into two divisions one of which is destined 
for parts in front of the spine, the other for parts behind it. 

The posterior roots of the nerves are distinguished from the anterior roots 
by their greater size, as well as by the greater thickness of the fasciculi of 
which they are composed. Each spinal nerve is furnished with a ganglion ; 
but the first cervical or sub-occipital nerve is in some cases without one. 
The size of the ganglia is in proportion to that of the nerves on which they 
are formed. 

The ganglia are in general placed in the intervertebral foramina, imme- 
diately beyond the points at which the roots perforate the dura mater lining 
the spinal canal. The first and second cervical nerves, however, which 
leave the spinal canal, over the laminae of the vertebrae, have their ganglia 
opposite those parts. The ganglia of the sacral nerves are contained in the 
spinal canal, that of the last nerve being occasionally at some distance from 
the point at which the nerve issues. The ganglion of the coccygeal nerve 
is placed within the canal in the sac of dura mater, and at a variable dis- 
tance from the origin of the nerve. 

Fig. 421. Fig. 421. DIFFERKS-T 

VIEWS OF A PORTION OP 
THE SPINAL CORD FROM 
THK CERVICAL REGION 
WITH THE ROOTS OF 
THE NERVES. Slightly 
enlarged. 

In A, the anterior sur- 
face of the specimen is 
shown, the anterior nerve- 
root of the right side 
being divided ; in I>, a 
view of the right side is 
given ; in C, tho upper 
surface is shown ; in D, 
the nerve-roots and gan- 
glion are shown from 
below. 1, the anterior 
median fissure ; 2, pos- 
terior median fissure ; 3, 
anterior lateral depres- 
sion, over which thu ante- 
rior nerve-roots are seen 
to spread ; 4, posterior 
lateral groove, into which 
the posterior roots are 
seen to sink ; 5, anterior 
roots passing the ganglion ; 
5', in A, the anterior root 
divided ; 6, the posterior roots, the fibres of which enter the ganglion, 6' ; 7, the uciled 
or compound nerve ; 7', the posterior primary branch seen in A and D, to be derived in 
part from the anterior and in part from the posterior root. 


The fibres of the po: terior root of the nerve divide into two bundles as they 
approach the ganglion, and the inner extremity of the oval-shaped ganglion 
is sometimes bilobate, the lobes corresponding to the two bundles of fibres. 




SIZE AND STRUCTURE. MODE OF DIVISION. 631 

These fibres in man and the mammalia appear to pass through the ganglion with- 
out union with its cells. The cells are both unipolar and bipolar, but the fibres con- 
nected with them all pass to the periphery (Kolliker), so that beyond the ganglion 
the posterior root of the nerve has received an additional set of fibres besides those 
which it contains before reaching the ganglion. In fishes, on the contrary, all the 
fibres of the posterior root are connected with the opposite extremities of the bipolar 
cells of the ganglion. 

The anterior roots of the spinal nerves are, as will be inferred from what 
has been already stated, the smaller of the two ; they are devoid of 
ganglioiiic enlargement, and their fibres are collected into two bundles near 
the intervertebral ganglion, as in the posterior root. 

Size, The roots of the upper cervical nerves are smaller than those of the 
lower nerves, the first being much the smallest. The posterior roots of 
these nerves exceed the anterior in size more than in the other spinal nerves, 
and they are likewise composed of fasciculi which are considerably larger 
than those of the anterior roots. 

The roots of the dorsal nerves, exception being made of the first, which 
resembles the lowest cervical nerves and is associated with the in in a part of 
its distribution, are of small size, and vary but slightly, or not at all, from 
the second to the last. The fasciculi of both roots are thinly strewed over 
the spinal cord, and are slender, those of the posterior exceeding in thickness 
tho^e of the anterior root in only a small degree. 

The roots of the lower lumbar, and of the upper sacral nerves, are the 
largest of all the spinal nerves ; those of the lowest sacral and the coccygeal 
nerve are, on the other hand, the slenderest. All these nerves are crowded 
together round the lower end of the corJ. Of these nerves the anterior 
roots are the smaller, but the disproportion between the anterior and pos- 
terior roots is not so great as in the cervical nerves. 

Length of the nerves in the spinal canal. The place at which the roots 
of the upper cervical nerves are connected with the spinal cord being nearly 
opposite the foramina by which they respectively leave the canal, these roots 
are comparatively short. But the distance between the two points referred 
to is gradually augmented from nerve to nerve downwards, so that the 
place of origin of the lower cervical nerves is the breadth of at least one 
vertebra, and that of the lower dorsal nerves about the breadth of two 
vertebrae above the foramina by which they respectively emerge from the 
canal. Moreover, as the spinal cord extends no farther than the first 
lumbar vertebra, the length of the roots of the lumbar, sacral, and coccygeal 
nerves increases rapidly from nerve to nerve, ami in each case may be 
estimated by the distance of the foramen of exit from the extremity of the 
cord. Owing to their length, and the appearance they present in connection 
with the spinal cord, the aggregation of the roots of the nerves last referred 
to has been named the " cauda equina." 

The direction the roots take within the canal requires brief notice. The 
first cervical nerve is directed horizontally outwards. The roots of the 
lower cervical and dorsal nerves at first descend over the spinal cord, held 
in contact with it by the arachnoid, till they arrive opposite the several 
iutervertebral foramina, where they are directed horizontally outwards. 
The nerves of the cauda equina run in the direction of the spinal canal. 

Division of the nerves. The two roots of each of the spinal nerves unite 
immediately beyond the ginglion, and the trunk thus formed separates, 
as already mentioned, into two divisions, an anterior and a posterior, which 
are called primary branches or divisions. 

In the detailed description of the spinal nerves which follows, we shall 



632 THE SPINAL NERVES. 

begin with their posterior primary divisions, calling attention first to certain 
characters common to the whole of them, and afterwards stating separately 
the arrangement peculiar to each group of nerves (cervical, dorsal, &c.) 



POSTERIOR PRIMARY DIVISIONS 

OF THE SPINAL NERVES. 

The posterior divisions of the spinal nerves are, with few exceptions, 
smaller than those given to the fore part of the body. Springing from the 
trunk which results from the union of the roots of the nerve in the inter- 
vertebral foramen, or frequently by separate fasciculi from each of the 
roots, each turns backwards at once, and soon divides into two parts, distin- 
guished as external and internal, distributed to the muscles and the integu- 
ment behind the spine. The first cervical, the fourth aud fifth sacral and 
the coccygeal nerve are the only nerves the posterior divisions of which do 
not separate into external and internal branches. 

THE SUBOCCIPITAL NERVE. The posterior division of the suboccipital 
nerve, which is the larger of the two primary divisions, emerging over the 
arch of the atlas, between this and the vertebral artery, enters the space 
bounded by the larger rectus and the two oblique muscles, and divides 
into branches for the surrounding muscles. 

a. One branch descends to the lower oblique muscle and gives a filament, through 
or over the fibres of that muscle, to join the second cervical nerve. 

6. Another ascends over the larger rectus muscle, supplying it and the smaller 
rectus. 

c. A third enters the upper oblique muscle. 

d. A fourth sinks into the complexus, where that muscle covers the nerve and its 
branches. 

A cutaneous branch is occasionally given to the back of the head ; it accompanies 
the occipital artery, and is connected beneath the integument with the great and 
small occipital nerves. 

Fig. 422. SUPERFICIAL AND DEEP DISTRIBUTION OP THE POSTERIOR PRIMARY DIVISIONS 
OF THE SPINAL NERVES (from Hirschfeld and Leveille). 

On the left side the cutaneous branches are represented as lying upon the superficial 
layer of muscles ; on the right side, the superficial muscles having been removed, the 
splenius and complexus have been divided in the neck, and the erector spinae separated 
and partially removed in the back, so as to expose the deep issue of the nerves. 

, a, lesser occipital nerve from the cervical plexus ; 1, external muscular branches of 
the first cervical nerve and union by a loop with the second ; 2, placed on the rectus 
capitis posticus major, marks the great occipital nerve passing round the short muscles 
and piercing the complexus : the external branch is seen to the outside ; 2', cranial dis- 
tribution of the great occipital ; 3, external branch of the posterior primary division of 
the third nerve ; 3', its internal branch, or third occipital nerve ; 4', 5', 6', 7', 8', 
internal branches of the several corresponding nerves on the left side : the external 
branches of these nerves proceeding to muscles are displayed on the right side : dl, io 
d 6, and thence to c? 12, external muscular branches of the posterior primary divisions of 
the twelve dorsal nerves on the right side ; d 1', to d 6', the internal cutaneous branches 
of the six upper dorsal nerves on the left side ; d 7', to d 12', cutaneous branches of the 
six lower dorsal nerves from the external branches ; Z, I, external branches of the pos- 
terior primary branches of several lumbar nerves on the right side piercing the muscles, 
the lower descending over the gluteai region ; I', l\ the same more superficially on the left 
side ; s, s, on the right side, the issue and union by loops of the posterior primary divisions 
of four sacral nerves ; s' t s', some of these distributed to the skin on the left side. 



POSTERIOR PRIMARY DIVISIONS. 



633 



Fig. 422. 




CERVICAL NERVES, with the exception of the saboccipital. The external 
branches give only muscular offsets, and are distributed to the splenius and 
the blender muscles prolonged to the neck from the erector spinse, viz., the 



634 THE SPINAL NERVES. 

cervicalis ascendens, and the trans versa! is colli with the trachelo-mastoid. 
That of the second nerve is the largest of the series of external branches, 
and is often united to the corresponding branch of the third ; it supplies 
the complexus muscle which covers it, and ends in the splenius and trachelo- 
inastoid muscles. 

The internal branches, larger than the external, are differently disposed at 
the upper and the lower parts of the neck. That of the second cervical 
nerve is named, from its size and destination, the great occipital, and 
requires separate notice. The rest are directed inwards to the spinous pro- 
cesses of the vertebrae. Those derived from the third, fourth, and fifth 
nerves pass over the semispinalis and beneath the complexus muscle, and, 
having reached the spines of the vertebrae, turn transversely outwards and 
are distributed in the integument over the trapezius muscle. From the 
cutaneous branch of the third nerve a branch passes upwards to the integu- 
ment on the lower part of the occiput, lying at the inner side of the great 
occipital nerve, and is sometimes called third occipital nerve. 

Between the inner branches of the first three cervical nerves, beneath the complexus, 
there are frequently communicating fasciculi ; and this communication Cruveilhier 
has designated as " the posterior cervical plexus." 

The internal branches from the lowest three cervical nerves are placed 
beneath the semispinalis muscle, and end in the muscular structure, without 
furnishing (except occasionally the sixth) any offset to the skin. These 
three nerves are the smallest of the series. 

The great occipital nerve is directed upwards on the lower oblique muscle, 
and is transmitted to the surface through the complexus and trapezius 
muscles, giving twigs to the complexus. Ascending with the occipital 
artery, it divides into branches, which radiate over the occipital part of the 
occipito-frontalis muscle, some appearing to enter the muscle, and others 
joining the smaller occipital nerve. 

An auricular branch is sometimes supplied to the back of the ear by the great 
occipital nerve. 

DORSAL NERVES. The external branches increase in size from above 
downwards. They are directed through or beneath the longissiinus dorsi to 
the space between that muscle and the ilio-costalis and accessory ; they supply 
both those muscles, together with the small muscles continued upwards from 
the erector spinse to the neck, and also the levatores costarum. The lower 
five or six nerves give cutaneous twigs, which are transmitted to the integu- 
ment in a line with the angles of the ribs. 

The internal branches of the upper six dorsal nerves appear in the interval 
between the multifidus spinee and the semispinalis dorsi ; they supply 
those muscles, and become cutaneous by the side of the spinous processes of 
the vertebras. The cutaneous branch from the second nerve, and sometimes 
others, reach as far as the scapula. The internal branches of the lower six 
dorsal nerves are placed between the multifidus spinso and longissimus dorsi, 
and end in the multifidus without giving branches to the integument. 
Where cutaneous nerves are supplied by the internal branches, there are 
none from the external branches of the same nerve, and vice versa. 

LUMBAR NERVES. The external branches enter the erector spinse, and 
give filaments to the intertrans verse muscles. From the upper three, 
cutaneous nerves are supplied ; and from the last, a fasciculus descends to 
the corresponding branch of the first sacral nerve. The cutaneous nerves 
given from the external branches of the first three lumbar nerves, pierce the 



ANTERIOR PRIMARY DIVISIONS. 635 

fleshy part of the ilio-costalis, and the apcmeurosis of the latissimus dorsi ; 
they cross the iliac crest near the edge of the erector spinse, and terminate 
in the integument of the gluteal region. One or more of the filaments may 
be traced as far as the great trochanter of the femur. 

The internal branches wind backwards in grooves close to the articular 
processes of the vertebrae, and sink into the mukifidus spinse muscle. 

SACRAL NERVES. The posterior divisions of the nerves, except the 
last, issue from the sacrum through its posterior foramina. The first three 
are covered at their exit from the bone by the multifidus spinre muscle, 
and bifurcate like the posterior trunks of the other spinal nerves ; but 
the remaining two, which continue below that muscle, have a peculiar 
arrangement, and require separate examination. 

The internal branches of the Jirst three sacral nerves are small, and are 
lost in the multifidus spinse muscle. 

The external branches of the same nerves are united with one another, 
and with the last lumbar and fourth sacral nerves, so as to form a series of 
anastomotic loops on the upper part of the sacrum. These branches are 
then directed outwards to the cutaneous or posterior surface of the great 
sacro-sciatic ligament, where, covered by the gluteus maximus muscle, they 
form a second series of loops, and end in cutaneous nerves. These pierce the 
great gluteus muscle in the direction of a line from the posterior iliac spine 
to the tip of the coccyx. They are commonly three in number one is 
near the innominate bone, another opposite the extremity of the sacrum, 
and the third about midway between the other two. All are directed out- 
wards over the great gluteal muscle. 

In six dissections by Ellis tliis arrangement was found to be the most frequent. 
The variations to which it is liable are these : the first nerve may not take part in 
the second series of loops, and the fourth may be associated with them. 

The posterior divisions of the last two sacral nerves are smaller than those 
above them, and are not divided into external and internal branches. They 
are connected with each other by a loop on the back of the sacrum, and the 
lowest is joined in a similar manner with the coccygeal nerve ; one or two 
small filaments from these sacral nerves are distributed behind the coccyx. 

COCCYGEAL NERVE. The posterior division of the coccygeal nerve is very 
small, and separates from the anterior primary portion of the nerve in the 
sacral canal. It is joined by a communicating filament from the last sacral 
nerve, and ends in the fibrous structure covering the posterior surface of the 
coccyx. 



ANTERIOR PRIMARY DIVISIONS 

OP THE SPINAL NERVES. 

The anterior primary divisions of the spinal nerves are distributed to the 
parts of the body situated in front of the vertebral column, including the 
limbs. They are, for the most part, ponsiderably larger than the posterior 
divisions. 

The anterior division of each spinal nerve is connected by one or two 
slender filaments with the sympathetic. Those of the cervical, lumbar, and 
sacral nerves form plexuses of various forms ; but those of the dorsal nerves 
remain for the most part separate one from another. 

T T 2 



636 THE CERVICAL NERVES AND PLEXUS. 



CERVICAL NERVES. 

The anterior divisions of the four upper cervical nerves form the cervical 
plexus. They appear at the side of the neck between the scalenus medius 
and rectus anticus major muscles. They are each connected by a commu- 
nicating filament with the first cervical ganglion of the sympathetic nerve, 
or with the cord connecting that ganglion with the second. 

The anterior divisions of the four lower cervical nerves, larger than those 
of the upper four, appear between the scaleni muscles, and, together with 
that of the first dorsal, go to form the brachial plexus. They are each 
connected by a filament with one of the two lower cervical ganglia of the 
sympathetic, or with the plexus on the vertebral artery. 

The anterior divisions of the first and second nerves require a notice 
separately from the description of the nerves of the cervical plexus. 

SUBOCCIPITAL NERVE. 

The anterior primary division of the first nerve runs forwards in a groove 
on the atlas, and bends downwards in front of the transverse process of that 
vertebra to join the second nerve. In this course forwards it lies beneath 
the vertebral artery, and at the inner side of the rectus lateralis muscle, to 
which it gives a branch. As it crosses the foramen in the transverse process 
of the atlas, the nerve is joined by a filament from the sympathetic ; and 
from the arch, or loop of the atlas, which it makes in front of the transverse 
process, branches are supplied to the two anterior recti muscles. Short 
filaments connect this part of the nerve with the pneumo-gastric, the hypo- 
glossal, and the sympathetic nerves. 

Valentin notices filaments distributed to the articulation of the occipital bone with 
the atlas, and to the mastoid process of the temporal bone. , 

SECOND CERVICAL NERVE. 

The anterior division of the second cervical nerve, beginning between the 
arches of the first two vertebrae, is directed forwards between their trans- 
verse processes, being placed outside the vertebral artery, and beneath the 
iutertransverse and other muscles fixed to those processes. In front of the 
intertransverse muscles the nerve divides into an ascending part, which 
joins the first cervical nerve, and a descending part to the third. 

V . 

CERVICAL PLEXUS. 

The cervical plexus is formed by the anterior divisions of the first four 
cervical nerves, and distributes branches to some of the muscles of the neck, 
and to a portion of the integument of the head and neck. It is placed 
opposite the first four vertebras, beneath the sterno-mastoid muscle, and rests 
against the middle scalenus muscle and the levator auguli scapuhe. The 
disposition of the nerves in the plexus is easily recognised. Each nerve 
except the first, branches into au ascending and a descending part : and 
these are united in communicating loojps with the contiguous nerves. From 
the union of the second and third nerves, superficial branches are supplied 
to the head and neck ; and from the junction of the third with the fourth, 
arise the cutaneous nerves of the shoulder and chest. Muscular and com- 
municating branches spring from the same nerves. 

The branches of the plexus may be separated into two sets a superficial 



THE CERVICAL PLEXUS. 



637 



and deep ; the superficial consisting of those which ramify over the cervical 
fascia, supplying the integument and some also the platysma ; the deep 
comprising branches which are distributed for the most part to the muscles. 
The superficial nerves may be subdivided into ascending and descending ; 
the deep nerves into an internal and external series. 



Fig. 423. DIAGRAMMATIC Fig 423. 

OUTLINE OP THE FIRST 
PARTS OP THE CERVICAL 
AND UPPER DORSAL 
NERVES, SHOWING THE 
CERVICAL AND BRACHIAL 
PLEXUSES. J 

The nerves are separated 
from tlie spinal cord at 
their origin and are sup- 
posed to be viewed from 
before. Cl, is placed op- 
posite the roots of the first 
cervical or suboccipital 
nerve, and the roman num- 
bers in succession from IF, 
to VIII, opposite the roots 
of the corresponding cer- 
vical nerves ; DI, is placed 
opposite to the roots of the 
first dorsal nerve, and II, 
and IK, opposite the second 
and third nerves ; the origin 
of the posterior primary 
branch is shown in all the 
nerves; of these p 2, indi- 
cates the great occipital 
from the second, and ^;3, 
the smallest occipital nerve 
from the third. In con- 
nection with the cervical 
plexus the following indica- 
tions are given ; 1, anterior 
primary branch of the 
first cervical nerve and loop 
of union with the second 
nerve ; 2, lesser occipital 
nerve proceeding in this 
case from the second cervi- 
cal nerve, more frequently 
from the second and third ; 
3, great auricular nerve 
from the second and third ; 

3', superficial cervical nerve from the third; 3 n, communicating branches to the descen- 
dens noni from the second and third ; 3 s, communicating to the spinal-accessory from the 
second, third, and fourth ; 4, supraclavicular and supraacromial descending nerves : 
the loops or arches of communication between the four upper cervical nerves, and between 
the fourth and fifth are shown ; 4', the phrenic nerve springing from the fourth and fifth 
nerves. In connection with the nerves of the brachial plexus and the remaining nerves 
the following indications are given V, to VIII 7 , and D', the five roots of the brachial 
plexus ; 5, the rhomboid nerve ; 5', suprascapular ; 5", posterior thoracic ; 6, nerve to the 
subclavius muscle; 7, 7, inner and outer anterior thoracic nerves; 8, 8', 8", upper and 
lower subscapular nerves. In the larger nerves proceeding to the shoulder and arm from 
the plexus, those of the anterior division are represented of a lighter shade, those belonging 
to the posterior division darker ; ec, external cutaneous or musculo-cutaneous ; ?/i, median; 
M, ulnar, ic, internal cutaneous ; w, nerve of Wrisberg ; r, musculo -spiral ; c, circum- 
flex ; i, intercostal nerves ; i', lateral branch of the same ; ih, intercosto-humeral nerves. 




Ill 



038 THE CERVICAL NERVES AND PLEXUS. 



I. SUPERFICIAL ASCENDING BRANCHES. 

SUPERFICIAL CERVICAL NERVE. 

This nerve takes origin from the second and third cervical nerves, turns 
forward over the sterno-mastoid about the middle, and, after perforating the 
cervical fascia, divides beneath the platysma myoides into two branches, 
which are distributed to the anterior and lateral parts of the neck. 

a. The upper branch gives an ascending twig which accompanies the external jugular 
vein, and communicates freely with the facial nerve (cervico-facial division) ; it is then 
transmitted through the platysma to the surface, supplying that muscle, and ramifies 
in the integument of the upper half of the neck on the fore part, filaments reaching as 
high as the lower maxilla. 

b. The lower branch likewise pierces the platysma, and is distributed below the 
preceding, its filaments extending in front as low as the sternum. 

The superficial cervical nerve may arise from the plexus in the form of two or more 
distinct branches. Thus Valentin describes three superficial cervical nerves, which he 
names superior, middle, and inferior. (" Sommerring v. Bau," &c.) 

While the superficial cervical nerve ramifies over the platysma myoides, the facial 
nerve is beneath the muscle. According to Valentin many anastomotic arches are 
formed on the side of the neck between those two nerves, as well as between the 
branches of the former, one with another. 

GREAT AURICULAR NERVE. 

This nerve winds round the outer border of the sterno-mastoid, and is 
directed obliquely upwards beneath the platysma myoides, between the 
muscle and the deep fascia of the neck, to the lobe of the ear. Here the 
nerve gives a few small branches to the face, and ends in the auricular 
and mastoid branches. 

a. The auricular branches are directed to the back of the external ear, on which 
they ramify, and are connected with twigs derived from the facial nerve. One 
of these branches reaches the outer surface of the ear by a fissure between the 
antihelix and the concha. A few filaments are supplied likewise to the outer part 
of the lobule. 

b. The mastoid branch is united to the posterior auricular branch of the facial 
nerve, and ascends over the mastoid process to the integument behind the ear. 

c. The facial branches of the great auricular nerve, which extend to the integu- 
ments of the face, are distributed over the parotid gland. Some slender filaments 
penetrate deeply through the substance of the gland, and communicate with the facial 
nerve. 

SMALL OCCIPITAL NERVE. 

The smaller occipital nerve varies in size, and is sometimes double. It 
springs from the second cervical nerve, and is directed almost vertically to 
the head along the posterior border of the sterno-mastoid muscle. Having 
perforated the deep fascia near the cranium, the small occipital nerve is 
continued upwards between the ear and the great occipital nerve, and ends 
in cutaneous filaments which extend upwards in the scalp ; it communicates 
with branches from the larger occipital nerve, as well as with the posterior 
auricular branch of the facial. It appears to supply sometimes the occipito- 
frontalis muscle. 

The auricular branch (ram. auricularis superior posterior) is distributed to the 
upper part of the ear on the posterior aspect, and to the elevator muscle of the auricle. 
This auricular branch is an offset from the great occipital nerve, when the small 
occipital is of less size than usual. 



STJPRACLAVICULAR NERVES. 639 

II. SUPERFICIAL DESCENDING BRANCHES. 

SUPRACLAVICULAR NERVES. 

The descending series of the superficial nerves are thus named. There 

Fig. 424. 




Fig. 424. VIEW OP THE SUPERFICIAL DISTRIBUTION OF THE NERVES PROCEEDING FROM 
TEE CERVICAL PLEXUS (from Sappey after Hirschfeld and Leveille). 

1, superficial cervical nerve; 2,2, descending branches of the same; 3, ascending 
branches ; 4, twigs uniting with the facial ; 5, great auricular nerve ; 6, its parotid 
branch ; 7, its external auricular branch ; 8, twig of the same which pierces the auricle 
to pass to its outer surface ; 9, branch to the deep surface of the pinna ; 10, its union 
with the posterior auricular of the facial nerve ; 11, small occipital nerve ; 12, its branch 
which unites with the great occipital nerve ; 13, a mastoid branch or second small occipital ; 
14, twigs from this to the back of the neck ; 15, 16, supraclavicular nerves; 17, 18, 
supraacromial nerves ; 19, branch of the cervical nerves passing into the trapezius muscle ; 
20, spinal accessory distributed to the same and receiving a uniting branch from the cervical 
nerves ; 21, branch to the levator scapuli ; 22, trunk of the facial nerve ; 23, its posterior 
auricular branch passing into the occipital and posterior and superior auricular muscles ; 
24, its cervico- facial branches. 



640 THE CERVICAL NERVES AND PLEXUS. 

are two of these nerves, or, in some cases, a greater number. They arise 
from the third and fourth cervical nerves, and descend in the interval 
between the sterno-mastoid and the trapezius muscles. As they approach 
the clavicle, the nerves are augmented to three or more iii number, and are 
recognised as internal, middle, and posterior. 

a. The internal (sternal) branch, which is much smaller than the rest, ramifies over 
the inner half of the clavicle, and terminates near the sternum. 

b. The middle branch, lying opposite the interval between the pectoral and deltoid 
muscles, distributes some twigs over the fore part of the deltoid, and others over 
the pectoral muscle. The latter join the small cutaneous branches of the intercostal 
nerves. 

c. The external or posterior branch (acromial) is directed outwards over the acro- 
mion, and the clavicular attachment of the trapezius muscle, and ends in the integu- 
ment of the outer and back part of the shoulder. 



III. DEEP BRANCHES : INNER SERIES. 

CONNECTING BRANCHES. 

The cervical plexus is connected near the base of the skull with the 
trunks of the pneumo-gastric, hypoglossal, and sympathetic nerves, by 
means of filaments intervening between those nerves and the loop formed 
by the first two cervical nerves in front of the atlas (p. 637). 

MUSCULAR BRANCHES. 

Branches to the anterior recti muscles proceed from the cervical nerves 
close to the vertebrae, including the loop between the first two of these 
nerves. 

Two branches to the ansa hypoglossi, one from the second, the other from 
the third cervical nerve, descend over or under the internal jugular vein, to 
form a loop of communication with the rarnus descendens noni, and aid in 
the supply of the muscles below the hyoid bone (p. 6 20). 

PHRENIC NERVE. 

The diaphragmatic or phrenic nerve passes down through the lower part 
of the neck and the thorax to its destination. 

It commences from the fourth cervical nerve, and receives usually a fasci- 
culus from the fifth. As it descends in the neck, the nerve is inclined 
inwards over the anterior scalenus muscle ; and near the chest it is joined 
by a filament of the sympathetic, and sometimes also by another filament 
derived from the fifth and sixth cervical nerves. 

As it enters the thorax each phrenic nerve is placed between the sub- 
clavian artery and vein, and crosses over the internal mammary artery near 
the root. It then takes nearly a straight direction, in front of the root of 
the lung on each side, and along the side of the pericardium, between 
this and the mediastinal part of the pleura. Near the diaphragm it divides 
into branches, which separately penetrate the fibres of that muscle, and then 
diverging from each other, are distributed on the under surface. 

The right nerve is placed more deeply than the left, and is at first directed 
along the outer side of the right innominate vein, and the descending vena 
cava. 



DEEP CERVICAL NERVES.- BRACIIIAL PLEXUS. 641 

The nerve of the left side is a little longer than that of the right, in conse- 
quence of the oblique position of the pericardium round which it winds, 
and also because of the diaphragm beiug lower on this than on the opposite 
side. This nerve crosses in front of the arch of the aorta and the pul- 
monary artery before reaching the pericardium. 

Besides the terminal branches supplied to the diaphragm, each phrenic nerve gives 
filaments to the pleura and pericardium ; and receives sometimes an offset from the 
union of the descendens noni with the cervical nerves. Swan notices this union as 
occurring only on the left side. Luschka describes twigs from the lower part of the 
nerve to the peritoneum, the inferior cava, and the right auricle of the heart. 

One or two filaments of the nerve of the right side join in a small ganglion with 
branches to the diaphragm which are derived from the solar plexus of the sympa- 
thetic ; and from the ganglion twigs are given to the suprarenal capsule, the hepatic 
plexus, and the lower vena cava. On the left side there is a junction between the 
phrenic and the sympathetic nerves near the oesophageal and aortic openings in the 
diaphragm, but without the appearance of a ganglion. 

IV. DEEP BRANCHES : EXTERNAL SERIES. 

Muscular branches. The sterno-mastoid receives a branch from the 
second cervical nerve. Two branches proceed from the third nerve to the 
levator anguli scapulas ; and from the third and fourth cervical nerves, as 
they leave the spinal canal, branches are given to the middle scalenus 
muscle. Further, the trapezius has branches prolonged to it ; and thus, 
like the sterno-mastoid, this muscle receives nerves from both the spinal 
accessory and the cervical plexus. 

Connection with the spinal accessory nerve. In the substance of the sterno- 
mastoid muscle, this nerve is connected with the branches of the cervical 
plexus furnished to that muscle. It is also connected with the* branches 
distributed to the trapezius the union between the nerves being beneath 
the muscle, and having the appearance of a plexus ; and with another 
branch of the cervical plexus in the interval between the two muscles. 

Summary of the cervical plexus. From the cervical plexus are distributed 
cutaneous nerves to the ba?k of the head, to part of the ear and face, to the 
anterior half of the neck, and to the upper part of the trunk. The muscles 
supplied with nerves from the plexus are the sterno-mastoid, the platysma, 
and the lower hyoid muscles in part ; the anterior recti, the levator anguli 
scapulse, the trapezius, the scalenus medius, and the diaphragm. By means 
of its branches the plexus communicates with the pneumo-gastric, spinal 
accessory, hypoglossal, and sympathetic nerves. 

BRACHIAL PLEXUS. 

This large plexus, from which the nerves of the upper limb are supplied, 
is formed by the union of the anterior trunks of the four lower cervical and 
first dorsal nerves ; and it further receives a fasciculus from the lowest of 
the nerves (fourth), which goes to form the cervical plexus. The plexus 
extends from the lower part of the neck to the axillary space, and termi- 
nates opposite the coracoid process of the scapula in large nerves for the 
supply of the limb. 

The manner in which the nerves are disposed in the plexus is liable to 
some variation, but the following may be regarded as the arrangement most 
frequently met with. The fifth and sixth cervical are joined at the outer 
border of the scalenus, and a little farther out receive the seventh nerve, 



642 



THE BEACHIAL PLEXUS. 



the three nerves giving rise to one large upper cord. The eighth cervical 
and first dorsal nerves are united in another lower cord whilst they are 

Fig. 425. 




Fig. 425. DEEP DISSECTION OF THE AXILLA, SHOWING THE BRACHIAL PLEXUS AND 
NEIOHBOUKING NERVES (from Sappey after Hirschfeld and Leveille). 

The clavicle has been sawn through near its sternal end, and is turned aside with the 
muscles attached to it ; the subclavius, and the greater and lesser pectoral muscles have 
been removed from the front of the axilla. 1, loop of union between the descendens noni 
and a branch of the cervical plexus ; 2, pneumo-gastric ; 3, phrenic passing down to the 
inner side of the scalenus anticus muscle ; 4, anterior primary division of the fifth cervical 
nerve ; 5, the same of the sixth ; 6, 7, the same of the seventh and eighth cervical nerves ; 
8, the same of the first dorsal nerve ; 9, 9, branch from the plexus to the subclavius 
muscle, communicating with the phrenic nerve; 10, posterior thoracic nerve distributed 
to the serratus magnus ; 11, upper anterior thoracic nerve passing into the great pectoral 
muscle ; 13, lower anterior thoracic distributed to the lesser pectoral ; 14, twig of com- 
munication between these two nerves ; 12, suprascapular nerve passing through the supra- 
scapular notch ; 15, lower of the two subscapular nerves ; 16, nerve of the teres major ; 
17, long subscapular, or nerve of the latissimus dorsi ; 18, accessory of the internal 
cutaneous nerve ; 19, union of the accessory cutaneous with the second and third inter- 
costal nerves ; 20, lateral branch of the secoud intercostal ; 21, second internal cutaneous 
or nerve of Wrisberg ; 22, internal cutaneous nerve ; 23, the ulnar nerve to the inside of 
the axillary artery, passing behind the vein, and having, in this case, a union with the 
upper division of the plexus ; 24, the median nerve immediately below the place where its 
two roots embrace the artery, which is divided above this place; 25, the musculo-cutaneous 
nerve passing into the coraco-brachialis muscle; 26, the musculo-spiral nerve passing 
behind the divided brachial artery. 



BRANCHES OF THE BRACHIAL PLEXUS. 



643 



between the scaleni muscles. The two cords thus formed lie side by side 
in the fore part of the plexus, and external to the first part of the axillary 
vessels.. At the same place, or lower down, a third intermediate or posterior 
cord is produced by the union of fasciculi from each of the other two cords, 
or separately from the nerves forming them. The three cords of which the 
plexus now consists, are placed, one on the outer side of the axillary artery, 
one on the inner side, and one behind that vessel, and are continued into 
the principal nerves for the arm. 

The two fasciculi which unite to form the intermediate of the three 
trunks are generally separated at a higher level than the formation of the 
two other trunks, but they are also frequently given off as low as the clavicle, 
or even farther down ; this gives rise to some varieties, more apparent than 
real. The seventh nerve also may give a branch to the cord below it. 

The branches proceeding from the plexus are numerous, and may be 
conveniently divided into two classes viz., those that arise above the 
clavicle, and those that take origin below the bone. 



BRANCHES ABOVE THE CLAVICLE. 

Above the clavicle there arise from the trunks of the brachial plexus, the 
posterior thoracic and supra scapular nerves, a nerve for the rhomboid 
muscles, another for the subclavius, irregular branches for the scaleni and 
longus colli, and a branch to join the phrenic nerve. 

The branches for the scaleni and longus colli muscles spring in an irregular manner 
from the lower cervical nerves close to their place of emergence from the vertebral 
foramina. 

The branch for the rhomboid muscles arises from the fifth nerve, and is directed 
backwards to the base of the scapula through the fibres of the middle scalenus and 
beneath the levator anguli scapulae. It is distributed to the deep surface of the 
rhomboid muscles, and gives sometimes a branch to the levator scapulae. 



Fig. 426. DISTRIBUTION OP 

TOE SUPRASCAPULAR AND 

CIRCUMFLEX NERVES (from 
HirschfeldandLeveille). | 



Fig. 426. 



1' 




a, the scalenus medius and 
posticus muscles ; b, levator 
anguli scapulae ; c, acromion ; 
d. deltoid muscle, of which 
the back part has been de- 
tached from the scapula and 
in part removed ; e, rhomboid 
muscle ; /, teres major ; g, la- 
tissimus dorsi ; 1 , the brachial 
plexus of nerves as seen from 
behind ; 1', the nerve of the 
levator scapulae and rhomboid 
muscles ; 2, placed on the 
clavicle, marks the supra- 
scapular nerve ; 3, its branch 
to the supraspinatus muscle ; 

4, branch to the infraspinatus ; 

5, placed on the back of the 
humerus below the insertion 

of the teres minor, marks the circumflex nerve passing out of the quadrangular interval ; 

6, its branch to the teres minor muscle ; 7, branches to the deep surface of the deltoid ; 
8, cutaneous branch to the back of the shoulder. 



644 



THE BRACHIAL PLEXUS. 



The nerve of the subdavius muscle, of small size, arises from the front of the cord 
which results from the union of the fifth and sixth cervical nerves. It is directed 
over the outer part of the subclavian artery to the deep surface of the subclavius 
muscle. This small nerve is commonly connected with the phrenic nerve in the neck 
or in the che-st, by means of a slender filament. 

Branch to join the phrenic nerve. This small and short branch is an offset from 
the fifth cervical nerve ; it joins the phrenic nerve on the anterior scalenus muscle. 

POSTERIOR THORACIC NERVE. 

The posterior thoracic nerve (nerve of the serratus magnus, external 
respiratory of Bell) is formed in the substance of the middle scalenus muscle 
by two roots, one from, the fifth and another from the sixth nerve, and reaches 
the surface of the scalenus lower than the nerve of the rhomboid muscles, 
with which it is often connected. It descends behind the brachial plexus 
on the outer surface of the serratus magnus, nearly to the lower border of 
that muscle, supplying it with numerous branches. 

SUPRASCAPULAR NERVE. 

The suprascapular nerve arises from the back of the cord formed by the 
union of the fifth and sixth nerves, and bends beneath the trapezius to the 
upper border of the scapula, where it passes between the muscles and the 
bone. Entering the supraspinous fossa of the scapula, through, the supra- 
scapular notch (beneath the ligament which crosses the notch), the supra- 
scapular nerve supplies two branches to the supraspinatus, one near the 
upper, the other near the lower part of the muscle ; and it then descends 
through the great scapular notch into the lower fossa, where it ends in the 
infraspinatus muscle. 

In the upper fossa of the scapula, a slender articular filament is given to the 
shoulder-joint, and in the lower fossa other twigs of the nerve enter the same joint 
and the substance of the scapula. 



BRANCHES BELOW THE CLAVICLE. 

Origin of nerves from the plexus. The several nerves now to be described 
are derived from the three great cords of the plexus in the following order. 

From the upper or outer cord, the external of the two anterior thoracic 
nerves, the musculo-cutaneous, and the outer root of the median. 

From the lower or inner cord, the inner of the two anterior thoracic, the 
nerve of Wrisberg, the internal cutaneous, the ulnar, and the inner root of 
the median. 

From the posterior cord, the subscapular nerves, the circumflex, and 
the musculo-spiral. 

The nerves traced to the spinal nerves. If the fasciculi of which the principal 
nerves are composed be followed through the plexus, they may be traced to those of 
the spinal nerves which in the subjoined table are named along with each trunk. 
The higher numbers refer to the cervical nerves, the unit to the dorsal nerve : 



5.6.7.8. 



Subscapular from 

Circumflex . 

Musculo-spiral . 

External cutaneous . 

Median 5.6.7.8.1. 



1. or 7.8.1. 



Ulnar 

Internal cutaneous . ) 

Small internal cutaneous ) 

outer 5.6.7 
inner 8.1. 



Anterior thoracic 



The outline in Fig. 423, taken from a dissection, represents one of the most 
common arrangements. 



ANTERIOR THORACIC. SUBSCAPULAR NERVES. 



645 



Some differences will be found in the statements of anatomists who have 
investigated the subject for instance, Scarpa (" Annotations Anatom.")and Kronen- 
berg (" Plex. nervor. Structura et Virtutes ") with respect to the nerves to which 
the branches are assigned. This difference is mainly owing to the variation which 
actually exists in different cases. 

ANTERIOR THORACIC NERVES. 

The anterior thoracic nerves, two in number, supply the pectoral 
muscles. 

The external, or more superficial branch, arising from the outer cord, 
crosses inwards over the axillary artery, and terminates in the great pectoral 
muscle. 

The internal, or deeper branch, springing from the inner cord, comes 
forwards between the axillary artery and vein to the small pectoral muscle, 
and is joined by a branch from the exterual. This nerve presents a plexi- 
form division beneath the small pectoral muscle, and supplies branches to 
it and the larger pectoral muscle. The two nerves are connected by a tila- 
ment which forms a loop over the artery at the inner side. 

SUBSCAPULAR NERVES. 

These nerves, three in number, take origin from 
the posterior cord of the plexus. 

The upper nerve, the smallest of the sub- 
scapular nerves, penetrates the upper part of the 
subscapular muscle. The lower nerve gives a 
branch to the subscapularis at its axillary border, 
and ends in the teres major muscle. There is 
sometimes a distinct nerve for the last-named 
muscle. 

The long subscapular nerve, the largest of the 
three, runs along the lower border of the sub- 
scapular muscle to the lutissinius dorsi, to which 
it is distributed. 

Fig. 427. DISTRIBUTION OF THE POSTKRIOR CUTANEOUS 
NERVES OP THE SHOULDER AND ARM (from Hirschfeld 
and Leveille). I 

1, supra-acromial branches of the cervical nerves de- 
scending on the deltoid muscle ; 2, ascending or reflected, 
and 2', descending cutaneous branches of the circumflex 
nerve ; 3, inferior external cutaneous of the musculo-spiral 
nerve ; 4, external and posterior cutaneous branches of the 
niusculo-cutaneous nerve to the forearm ; 5, internal 
cutaneous of the musculo-spiral ; 6, intercosto-humeral 
branches ; 7, twigs of the nerve of Wrisberg ; 8, upper 
posterior branch of the internal cutaneous nerve ; 9, lower 
branch of the same. 

CIRCUMFLEX NERVE. 

The circumflex or axillary nerve gives both 
muscular and cutaneous nerves to the shoulder. 
Springing from the posterior cord, this nerve is at 
first placed behind the axillary artery, but at the 
lower border of the subscapular muscle it is inclined backwards with the 
posterior circumflex artery, in the space between the scapula and tere& 




646 THE BRACHIAL PLEXUS. 

major muscle above the long head of the triceps, and separates into an 
upper and a lower branch, which are distributed to the deltoid and teres 
minor muscles, the integument of the shoulder, and the shoulder-joint. 

a. The upper portion winds round the upper part of the humerus, extending to the 
anterior border of the deltoid muscle, to which it is distributed. One or two 
cutaneous filaments, penetrating between the muscular fibres, are bent downwards 
and supply the integument over the lower part of the muscle. 

b. The lower branch supplies offsets to the back part of the deltoid, and furnishes 
the nerve to the teres minor, which is remarkable in presenting a gangliform enlarge- 
ment. It then turns round the posterior border of the deltoid below the middle, and 
ramifies in the integument over the lower two-thirds of that muscle, one branch 
extending to the integument over the long end of the triceps muscle. 

c. An articular filament for the shoulder-joint arises near the commencement of 
the nerve, and enters the capsular ligament below the subscapular muscle. 

INTERNAL CUTANEOUS NERVE. 

At its origin from the inner cord of the brachial plexus, this nerve is 
placed on the inner side of the axillary artery. It becomes cutaneous about 
the middle of the arm, and after perforating the fascia, or, in some cases, 
before doing so, is divided into two parts ; one destined for the anterior, 
the other for the posterior surface of the forearm. 

a. The anterior branch crosses at the bend of the elbow behind (in some cases 
over) the median basilic vein, and distributes filaments in front of the forearm, as 
far as the wrist; one of these is, in some instances, joined with a cutaneous branch 
of the ulnar nerve. 

b. The posterior branch inclines obliquely downwards at the inner side of the basilic 
vein, and winding to the back of the forearm, over the prominence of the internal 
condyle of the humerus, extends somewhat below the middle of the forearm. Above 
the elbow this branch is connected with the smaller internal cutaneous nerve (nerve 
of Wrisberg), and afterwards communicates with the outer portion of the internal 
cutaneous, and, according to Swan, with the dorsal branch of the ulnar nerve. 

c. A branch to the integument of the arm pierces the fascia near the axilla, and 
reaches to, or nearly to the elbow, distributing filaments outwards over the biceps 
muscle. This branch is often connected with the intercosto -humeral nerve. 

SMALL INTERNAL CUTANEOUS NERVE. 

The smaller internal cutaneous nerve, or nerve of Wrisberg, destined for 
the supply of the integument of the lower balf of the upper arm on the 
inner and posterior aspect, commonly arises from the inner cord of the 
brachial plexus in union with the larger internal cutaneous and uluar 
nerves. In the axilla it lies close to the axillary vein, but it soon appears 
on the inner side of that vessel, and communicates with the intercosto- 
humeral nerve. It then descends along the inner side of the brachial 
vessels to about the middle of the arm, where it pierces the fascia, and its 
filaments are thence continued to the interval between the internal condyle 
of the humerus and the olecranon. 

Branches. In the lower third of the arm, branches of this small nerve are directed 
almost horizontally to the integument on the posterior aspect ; and the nerve ends 
at the elbow by dividing into several filaments some of which are directed forwards 
over the inner condole of the humerus, while others are prolonged downwards 
behind the olecranon. 

Connection with the intercosto-humeral nerve. This connection presents much 
variety in different cases : in some, there are two or more intercommunications, form- 
ing a kind of plexus on the posterior boundary of the axillary space ; in others, the 



NERVES OF THE UPPER LIMB. 



647 



intercosto-humeral nerve is of larger size than usual, and takes the place of the nerve 
of Wrisberg, only receiving in the axilla a small filament from the brachial plexus ; 

Fig. 429. 





Fig. 428. ANTERIOR CUTANEOUS NERYES OF THE SHOULDER AND ARM (from Sappey after 
Hirschfeld and Leveilld). I 

1, 1, snpraclavicular and supraacromial nerves from the cervical plexus ; 2, 2, 2, 
cutaneous branches of the circumflex nerve ; 3, 4, upper branches of the internal cuta- 
neous nerve ; 5, superior external cutaneous branch of the musculo- spiral ; 6, internal 
cutaneous nerve piercing the deep fascia ; 7, posterior branch ; 8, communicating twig 
with one of the anterior branches ; 9, 10, anterior branches of this nerve, some turning 
round the median basilic and ulnar veins ; 11, musculo-cutaneous nerve descending over 
the median cephalic vein ; 12, inferior cutaneous branch of the musculo-spiral nerve. 

Fig. 429. ANTERIOR CUTANEOUS NERVES OP THE FOREARM AND HAND (from Sappey 
after Hirschfeld and Leveille). fe 

9, 10, 13, distribution of the anterior branches of the internal cutaneous nerve; 14, 
union of one of these with a twig of the ulnar nerve ; 12, inferior cutaneous branch of 
the musculo-spiral nerve; 11, 15, distribution of the external cutaneous nerve; 16, 
union of one of its branches with 17, the terminal branch of the radial nerve ; 18, 
palmar cutaneous branch of the median nerve; 19, 20, internal and external collateral 
branches to the thumb from the median nerve ; 21, external collateral to the index 
finger ; 22, 23, collateral branches to the index, middle and fourth fingers ; 24, 25, 
collateral branches from the ulnar nerve to the fourth and fifth fingers ; the network of 
communicating twigs formed by the terminal branches of these cutaneous nerves is repre- 
sented at the extremities of the fingers. 



648 NER\ES OF THE UPPER LIMB. 

and this small communicating filament represents in such cases the nerve of 
Wrisberg. 

MUSCULO-CUTANEOUS NERVE. 

The musculo-cutaneous or external cutaneous nerve (perforans Casserii) in 
deeply placed between the muscles as far as the elbow, and below that point 
is immediately under the integument. Arising from the brachial plexus 
opposite the small pectoral muscle, it perforates the coraco-brachialis muscle, 
and, passing obliquely across the arm between the biceps and brachialis 
anticus muscles, reaches the outer side of the biceps a little above the 
elbow. Here it perforates the fascia, and nearly opposite the elbow-joint it 
passes behind the median-cephalic vein, and, inclining outwards, divides 
into two branches which supply the integument on the outer side of the 
forearm, one on the anterior, the other on the posterior aspect. 

A. Branches in the arm : 

a. A branch to the coraco-brachialis and short head of the biceps is given off before 
the nerve pierces the former muscle ; and other filaments are furnished to the coraco- 
brachialis, while the nerve lies among its fibres. 

b. Branches to the biceps and brachialis anticus are given off while the nerve is 
between those muscles. 

c. Small filaments are given to the humerus and elbow-joint. 

B. Branches in the forearm : 

a. The anterior branch descends near the radial border of the forearm. It is 
placed in front of the radial artery near the wrist, and distributes some filaments 
over the ball of the thumb. Piercing the fascia, it accompanies the artery to the 
back part of the carpus. This part of the nerve is connected at the wrist with a 
branch of the radial nerve. 

b. The posterior branch is directed outwards to the back of the forearm, and 
ramifies in the integument of the lower third, extending as far as the wrist. It com- 
municates with a branch of the radial nerve, and with the external cutaneous branch 
of the musculo-spiral nerve. 

Summary. The musculo-cutaneous nerve supplies the coraco-brachialis, 
biceps, and brachialis anticus muscles, and the integument on the outer 
side of the forearm. Communications are established between it and the 
radial and the external cutaneous branch of the musculo-spiral. 

Varieties. In some cases it does not perforate the coraco-brachialis 
muscle. It is frequently found to communicate by a cross branch with or to 
be an offset of the median nerve ; and in the latter case, the coraco-brachialis 
muscle receives a separate branch from the brachial ploxus, which may be 
explained thus, that the main part of the musculo-cutaneous nerve, instead 
of piercing the coraco-brachialis muscle, remains adherent to the outer root 
and trunk of the median. 

ULNAR NERVE. 

The ulnar nerve, the largest branch of the inner cord of the brachial 
plexus, descends on the inner side of the artery of the limb as far as the 
middle of the arm, then turns backwards through the internal intermuscular 
septum with the inferior profunda artery, to reach the interval between the 
olecranon and the inner condyle of the humerus. From the axilla to this 
place it is covered only by the fascia, and it may be felt through the integu- 
ment a little above the elbow. It here passes between the two heads of 
the flexor carpi ulnaris, and it remains concealed by that muscle as far as the 
middle of the forearm ; it thence extends in a straight course along the' 
outer margin of the muscle, between it and the uluar artery, to the outer 



ULXAR AXD MEDIAN XEEVES. 649 

side of the pisiform bone. Above the wrist it gives off a large dorsal branch 
to the hand, and continuing onwards it enters the palm on the surface of 
the annular ligament, and divides into muscular and cutaneous branches. 
The ulnar nerve gives off no branches in the upper arm. 

A. Branches in the forearm : 

a. Articular filaments are given to the elbow-joint as the nerve passes behind it. 
Some filaments are also given to the wrist-joint. 

b. Muscular branches. One branch enters the upper part of the flexor carpi 
ulnaris, and another supplies the two inner divisions of the deep flexor of the fingers.* 

c. Cutaneous branches to the forearm. These two small nerves arise about the 
middle of the forearm by a common trunk. One pierces the fascia, and turning 
downwards, joins a branch of the internal cutaneous nerve. This branch is often 
absent. The second, a palmar branch, lies on the ulnar artery, which it accompanies 
to the hand. This little nerve gives filaments around the vessel, and ramifies in the 
integument of the hand, joining in some cases with other cutaneous offsets of the 
ulnar or median nerve. 

d. Dorsal branch to the hand. This, large offset, leaving the trunk of the ulnar 
nerve two or three inches above the wrist, winds backwards beneath the flexor carpi 
ulnaris and divides into branches ; one of these ramifies on the inner side of the 
little finger, another divides to supply the contiguous sides of that finger and the 
ring finger, while a third joins on the back of the metacarpus with the branch of the 
radial nerve which supplies the contiguous sides of the ring and middle finger. The 
several posterior digital nerves, now described, are united with twigs directed back- 
wards from the anterior digital nerves of the same fingers. 

B. Palmar branches: 

a. The deep branch separates from the trunk beyond the annular ligament, and, 
dipping down through the muscles of the little finger in company with the deep 
branch of the ulnar artery, it follows the course of the deep palmar arch across the 
hand. It supplies the short muscles of the little finger as it pierces them ; and as it 
lies across the metacarpal bones, it distributes two branches to each interosseous 
space one for the palmar, the other for the dorsal interosseous muscle, and supplies 
filaments to the two innermost lumbricales muscles. Opposite the space between the 
thumb and the index finger the nerve ends in branches to the adductor pollicis, and 
the inner head of the flexor brevis pollicis. 

b. The remaining part of the nerve supplies a branch to the palmaris brevis muscle 
and small twigs to the integument, and divides into two digital branches. 

Digital nerves. One of these belongs to the ulnar side of the little finger. The 
other is connected in the palm of the hand with a digital branch of the median nerve, 
and at the cleft between the little and ring fingers, divides into the collateral nerves 
for these fingers. The terminal disposition of the digital branches on the fingers is 
the same as that of the median nerve, to be presently described. 

Summary. The ulnar nerve gives cutaneous filaments to the lower part 
of the forearm (to a small extent), and to the hand on its palmar and 
dorsal aspects. It supplies the following muscles, viz., the ulnar flexor of 
the carpus, the deep flexor of the fingers (its inner half), the short muscles 
of the little finger with the palmaris brevis, the interosseous muscles of the 
hand, the two internal lumbricales, the adductor pollicis and the inner 
half of the flexor brevis pollicis. Lastly, it contributes to the nervous 
supply of the elbow and wrist joints. 

MEDIAN NERVE. 

The median nerve arises by two roots, one from the outer, the other from 
the inner cord of the brachial plexus. Commencing by the union of these 

* A case has been recorded in which tlie ulnar nerve supplied also two branches to the 
flexor sublimis digitorum (Turner, " Kat. Hist. Review," 1864). 

u u 



650 



NERVES OF THE UPPER LIMB. 

Fig. 430. Fig. 431. 




10 




Fig. 430. DEEP VIEW OP THE ANTERIOR NERVES OP THE SHOULDER AND ARM (from 
Sappey aiter Hirschfeld and Leveille). | 

1, musculo-cutaneous nerve ; 2, its twig to the coraco-brachialis muscle ; 3, its branch 
to the biceps; 4, its branch to the brachialis anticus ; 5, twig of union with the median 
nerve (a variety) ; 6, continuation of the nerve in its cutaneous distribution ; 7, musculo- 
spiral nerve in the interval between the brachialis anticus and supinator longus ; 8, inferior 
external cutaneous branch of the musculo-spiral ; 9, the internal cutaneous and small 
internal cutaneous nerves divided ; 10, anterior branch of the internal cutaneous; 11, 
median nerve ; to the inside the ulnar nerve is crossed by the line from 11. 



Fig. 431. DEEP VIEW OP THE ANTERIOR NERVES OF THE FOREARM AND HAND (from 
Sappey after Hirschfeld and Leveille). 

12, the median nerve ; 13, its branches to the pronator teres ; 14, branch to the super- 
ficial flexor muscles, which have been removed ; 15, branch to the flexor digitorum pro- 
fund us ; 16, branch to the flexor longus pollicis ; 17, anterior interosseous branch; 18, 
cutaneous palmar branch cut short; 19, branches to the short muscles of the thumb ; 
20, 21, collateral branches to the thumb; 22, 23, 24, collateral branches to the second, 
third, and fourth fingers ; 25, branch given by the ulnar nerve to the flexor carpi ulnaris ; 
26, branch to the flexor digitorum profundus ; 27, cutaneous communicating twig ; 28, 
dorsal branch of the ulnar ; 29, superficial palmar branch ; 30, 31, collateral branches 
to the fourth and fifth fingers ; 32, deep palmar branch ; 33, its branch to the short 
muscles of the little finger ; 34, 35, 36, twigs given by the deep branch of the ulnar to 
the third and fouith lurnbricales, all the interossei, and the adductor pollicis. 



BRANCHES OF THE MEDIAN NERVE. 651 

roots in front or on the outer side of the axillary artery, the nerve descends 
in contact with the brachial artery, gradually passing inwards over it, 
and near the elbow is at the inner side of the vessel. Crossing the bend of 
the arm it passes beneath the pronator radii teres, separated by the deep slip 
of that muscle from the ulnar artery, and continues straight down the front 
of the forearm, between the flexor sublimis digitorum and flexor profundus. 
Arrived near the wrist it lies b.neath the fascia, between the tendons of the 
flexor sublimis and that of the flexor carpi radialis. It then enters the 
palm behind the annular ligament, and rests on the flexor tendons. Some- 
what enlarged, and of a slightly reddish colour, it here separates into two 
parts of nearly equal size. One of these (the external) supplies some 
of the short muscles of the thumb, and gives digital branches to the thumb 
and the index finger ; the second portion supplies the middle finger, and. 
in part the index and ring fingers. 

The median nerve gives no branch to the upper arm. 

A. Branches in the forearm : 

In the forearm the median nerve supplies muscular branches, and, near 
the wrist, a single cutaneous filament. All the muscles on the front of the 
f jrearm (pronators and flexors), except the flexor carpi ulnaris and part of 
the deep flexor of the fingers, are supplied from this nerve. 

a. The branches for the superficial muscles are separate twigs given off from the 
nerve below or near the elbow-joint, but the branch furnished to the pronator teres 
often arises above the joint. 

b. Anterior interosseous nerve. This is the longest branch of the median nerve, 
and it supplies the deeper muscles of the forearm. Commencing at the upper part 
of the forearm, beneath the superficial flexor of the fingers, it passes downwards 
with the anterior interosseous artery on the interosseous membrane, and between 
the long flexor of the thumb and the deep flexor of the fingers, to the pronator 
quadratus muscle, in which it ends. 

c. The cutaneous palmar branch pierces the fascia of the forearm close to the 
annular ligament, and, descending over that ligament, ends in the integument of the 
palm about the middle : being connected by a twig with the cutaneous palmar branch 
of the ulnar nerve. It distributes some filaments over the ball of the thumb, which 
communicate with twigs of the radial or the external cutaneous nerve. 

B. Branches in the hand : 

a. Branch to muscles of the thumb. This short nerve subdivides into branches 
for the abductor, the opponens, and the outer head of the flexor brevis pollicis muscle. 

b. Digital nerves. These are five in number, and belong to the thumb, and the 
fingers as far as the outer side of the ring-finger. As they approach the clefts 
between the fingers, they are close to the integument in the intervals between the 
longitudinal divisions of the palmar fascia. 

The first and second nerves lie along the sides of the thumb ; and the former (the 
outer one) is connected with the radial nerve upon the ball of the thumb. 

The third, destined for the radial side of the index finger, gives a muscular branch 
to the first or most external lumbrical muscle. 

The fourth supplies the second lumbricalis, and divides into branches for the 
adjacent sides of the index and middle fingers. 

The fifth, the most internal of the digital nerves, is connected by a crossing-twig 
with the ulnar nerve, and divides to furnish branches to the adjacent sides of the 
ring and middle fingers. 

Each digital nerve divides at the end of the finger into two branches, one 
of which supplies the ball on the fore part of the finger ; the other ramifies 
in the pulp beneath the nail. Branches pass from each nerve forwards and 
backwards to the integument of the finger; and one larger than the rest 

u u 2 




652 NERVES OF THE UPPER LIMB. 

inclines backwards by the side of the first phalanx of the finger, and, after 
joining the dorsal digital nerve, ends in the integument over the last 
phalanx. 

Fig 432 Fi" 432. DISTIUBUTION OP THE DIGITAL NERVES (from Hirschfeld and 

Leveille). 4 

1, palmar collateral nerve ; 2, its final palmar distribution ; 3, its 
dorsal or ungual distribution, and between these numbers the network of 
terminal filaments ; 4, collateral dorsal nerve ; 5, uniting twigs passing 
between the dorsal and palmar digital nerves. 

Summary. The median nerve gives cutaneous branches to 
the palm, and to several fingers. It supplies the proiiator 
muscles, the flexors of the carpus and the long flexors of the 
fingers (except the ulnar flexor of the carpus, and part of the 
deep flexor of the fingers), likewise the outer set of the short 
muscles of the thumb, and two lumbricales. 

Some similarity will be observed between the course and 
distribution of the median and ulnar nerves. Neither gives 
any offset in the arm. Together they supply all the muscles 
in front of the forearm and in the hand, and together they supply the 
skin of the palmar surface of the hand, and impart tactile sensibility to all 
tho fingers. 

MUSCULO-SPIRAL NERVE. 

The musculo-spiral nerve, the largest offset of the brachial plexus, 
occupies chiefly the back part of the limb, and supplies nerves to the ex- 
tensor muscles, as well as to the skin. 

Arising behind the axillary vessels from the posterior cord of the brachial 
plexus, of which it is the principal continuation and the only one prolonged 
into the arm, it soon turns backwards into the musculo-spiral groove, and, 
accompanied by the superior profunda artery, proceeds along that groove, 
Vet ween the humerus and the triceps muscle, to the outer side of the limb. It 
then pierces the external intermuscular septum, and descends in the interval 
between the supinator longus and the braohialis anticus muscle to the level of 
the outer condyle of the humerus, where it ends by dividing into the radial 
and posterior interosseous nerves. Of these, the radial is altogether a cuta- 
neous nerve, and the posterior interosseous is the muscular nerve of the back 
of tho forearm. 

The branches of the musculo-spiral nerve may be classified according as 
they arise on the inner side of the humerus, behind that bone, or on the 
outer side. 

A. Internal branches : 

(a) Muscular branches for the inner and middle heads of the triceps. That for 
the inner portion of the muscle is long and slender; it lies by the side of the ulnar 
nerve, and reaches as far as the lower third of the upper arm. One branch, previously 
noticed by authors, but more particularly described by Krause, is named by him the 
ulnar collateral branch.. It arises opposite the outer border of the latissimus dorsi 
tendon, and descends within the sheath of the ulnar nerve, through the internal 
intermuscular septum, and is distributed to the short inferior fibres of the triceps 
(Reichert and Du Bois Reymond's Archiv. 1864). 

(b) The internal cutaneous branch of the musculo-spiral nerve, commonly united in 
origin with the preceding, winds backwards beneath the intercosto-humeral nerve, 
and after supplying filaments to the skin, ends about two inches from the olecranon ; 



MUSCULO-SPIRAL,- RADIAL XERVE. 



653 



in some instances extending as far as the olecranon. This nerve is accompanied by a 
small cutaneous artery. 

.B. Posterior branches : 

These consist of a fasciculus of muscular branches which supply the outer head of the 
triceps muscle and the anconeus. The branch of the anconeus is slender, and remark- 
able for its length; it descends in the substance of the triceps to reach its destination. 

C. External branches : 

(a) The muscular branches supply the supinator longus, extensor carpi radialis 
longior, (the extensor carpi radialis brevior receiving its nerve from the posterior 
interosseous,) and occasionally give a small branch to the brachialis anticus. 

(6) The external cutaneous branches, two in number, arise where the nerve pierces 
the external intermuscular septum. 

The upper branch, the smaller of the two, is directed downwards to the fore part 
of the elbow, along the cephalic vein, and distributes filaments to the lower half of 
the upper arm on the anterior aspect. The lower branch extends as far as the wrist, 
distributing offsets to the lower half of the arm, and to the forearm, on their pos- 
terior aspect, and is connected near the wrist with a branch of the external cutaneous 



Fig. 433. DORSAL CUTANEOUS NERVES 
OP THE HAND. J 

The distribution delineated in this 
figure is not the most common, there being 
a larger than usual branch of the ulnar 
nerve : 1, the radial nerve descending 
beside the principal radial cutaneous vein ; 
2, and 3, dorsal branches to the two sides 
of the thumb ; 4, branch to the radial 
side of the forefinger ; 5, branch to the 
fore finger and middle finger, communi- 
cating with one from the ulnar nerve; 

6, the posterior branch of the ulnar nerve ; 

7, communicating twig ; 8, collateral 
branch to the middle and ring fingers ; 
9, collateral branch to the ring and little 
fingers ; 10, branch to the inner side of 
the hand and little finger. 



RADIAL NERVE. 

The radial nerve, continuing 
straight down from the musculo- 
spiral, is concealed by the long 
supinator muscle, and lies a little 
to the outer side of the radial 
artery. This position beneath the 
supinator is retained to about three 
inches from the lower end of the 
radius, where the nerve turns back- 
wards beneath the tendon of the 
muscle, -and becomes subcutaneous. 
It then separates into two branches, 
which ramify in the integument on 

the dorsal aspect of the thumb and the next two fingers in the following 
manner. 




654 



NERVES OF THE TIPPER LIMB. 



(a) The external branch extends to the radial side of the thumb, and is joined by an 
offset of the external cutaneous nerve. It distributes filaments over the ball of the 
thumb. 

(b) The internal portion communicates with a branch of the external cutaneous 
nerve on the back of the forearm, and divides into digital branches ; one running 
along the ulnar side of the thumb, a second on the radial side of the index finger, a 
third dividing to supply the adjacent sides of the index and middle fingers, while a 
fourth joins with an offset from the dorsal branch of the ulnar, and along with it 
forms a branch for the supply of the contiguous sides of the middle and ring 
fingers. These branches communicate on the sides of the fingers with the palmar 
digital nerves. 

Sometimes the interspace between the middle and ring fingers is entirely supplied 
by the radial, and at other times entirely by the ulnar nerve. 

POSTERIOR INTEROSSEOUS NERVE. 

This nerve, the larger of the two divisions of the musculo-spiral nerve, 
winds to the back of the forearm through the fibres of the supinator brevis 



Fig. 434. 



Fig. 434. VIEW OP THE RADIAL SIDE OP THE FORE-ARM, 

SHOWING THE FINAL DISTRIBUTION OF THE MuSCULO- 

SPIRAL NERVE (from Hirschfeld and Leveille). 5 

The supinator longus, andextensores carpi radiales longior 
and brevior have been divided, and their upper parts re- 
moved ; the extensor communis digitorurn is pulled back- 
wards by a hook, and the supinator brevis has been par- 
tially dissected to show the posterior interosseous nerve 
passing through it. 

1, placed upon the tendon of the biceps muscle, points 
to the musculo-cutaneous nerve ; 1', near the wrist, the 
lower part of this nerve and its plexus of union with the 
radial nerve ; 2, trunk of the musculo-spiral nerve emerg- 
ing from between the brachialis anticus, on which the 
number is placed, and the supinator longus muscle ; 2', 
its muscular twigs to the long supinator and long radial 
extensor of the carpus ; 2", the posterior interosseous nerve 
passing through the substance of the supinator brevis : 3, 
placed upon the cut lower portion of the supinator longus, 
the radial nerve ; 4, the external collateral nerve of the 
thumb ; 5, the common collateral of the fore-finger and 
thumb ; 6, the common collateral of the fore-finger and 
middle finger ; 7, the twig of union with the dorsal branch 
of the ulnar nerve ; 8, placed upon the common extensor 
of the fingers, the muscular branches of the posterior inter- 
osseous nerve to the long extensor muscles ; 9, upon the 
extensor secundi internodii pollicis, the branches to the 
short extensor muscles. 



muscle, and is prolonged between the deep and 
superficial layers of the extensor muscles to the 
interosseous membrane, which it approaches about 
the middle of the forearm. 

Much diminished in size by the separation of 
numerous branches for the muscles, the nerve lies 
at the lower part of the forearm beneath the 
extensor of the last phalanx of the thumb and 
the tendons of the common extensor of the 
fingers, and terminates on the back of the 

carpus in a gangliform enlargement, from which filaments are given to the 

adjoining ligaments and articulations. 




ANTERIOR DIVISIONS OF THE DORSAL NERVES. 655 

The branches of the interosseous nerve enter the surrounding muscles, 
viz., the extensor carpi radialis brevior and supinator brevis, the superficial 
layer of the extensor muscles except the anconeus, and the deep layer of 
the same muscles : that is to say, the nerve supplies the supinators, and 
the extensors of the carpus and fingers, with the exception of the supiuator 
longus and the extensor carpi radialis longior. 

Summary of the Musculo-spiral Nerve. 

The trunk of the nerve distributes its branches to the extensor muscles of 
the elbow-joint exclusively, with the exception of a filament to the brachialis 
anticus, which however receives its principal nerves from another source. 
Before separating into its two larga divisions, the nerve gives branches 
to two muscles of the forearm, viz., the long supiuator, and the long 
radial extensor of the carpus. The posterior iuterosseous division distri- 
butes nerves to the remaining muscles on the outer and back part of the 
forearm, except the anconeus (previously supplied), viz. , to the short supinator 
and the extensors. 

Cutaneous nerves are distributed, from the trunk of the nerve and its 
radial division, to the lower part of the upper arm, to the forearm, and to 
the hand on the posterior and outer aspect of each. 

ANTERIOR PRIMARY DIVISIONS OF THE DORSAL NERVES. 

These nerves are twelve in number, and, with the exception of the larger 
part of the first of them, which joins the brachial plexus, they are dis- 
tributed to the walls of the thorax and abdomen. Eleven of the nerves so 
distributed are termed intercostal, and the twelfth is situated below the last 
rib. The cords connecting them with the sympathetic nerve, placed close to 
the vertebrae, are very short. 

The anterior divisions of these nerves pas3 separately to their destination, 
without forming any plexus by the connection or interlacement of their 
fibres, and in this respect they differ from those of the other spinal nerves. 
From the iutervertebral foramina they are directed transversely across the 
trunk, and nearly parallel one to another. The upper six nerves, with the 
exception of the first, are confined to the parietes of the thorax ; while the 
lower six nerves are continued from the intercostal spaces to the muscles 
and integument of the anterior wall of the abdomen. 

FIRST DORSAL NERVE. 

The greater part of the anterior division of this nerve ascends over the 
neck of the first rib and the first intercostal artery to enter into the brachial 
plexus. The remaining portion of the nerve is continued as the first inter- 
costal, a small branch which courses along the first intercostal space, in the 
manner of the other intercostal nerves, but has usually no lateral cutaneous 
branch, and may also want the anterior cutaneous. 

UPPER, OR PECTORAL INTERCOSTAL NERVES. 

In their course to the fore part of the chest, these nerves accompany the 
intercostal blood-vessels. After a short space they pass between the internal 
and external intercostal muscles, supplying them with twigs, and, about 
midway between the vertebrae and the sternum, give off the lateral cutaneous 
branches. The nerves, greatly diminished, are now continued forwards 
amid the fibres of the internal intercostal muscles as far as the costal 
cartilages, where they come into contact with the pleura. In approaching 



656 



THE DORSAL NERVES. 
F ; c. 4C5. 




Fig. 435. VIEW OF THE ANTERIOR DIVISIONS OP THE DORSAL AND SOME OF THE OTIIEK 
SPINAL NERVES PROM BEFORE (from Hirscbfeld and LeveiHe"). 

The pectoralis major and minor muscles have been removed ; on the right side the 
rectus abdominis and internal oblique muscles are shown, on the left side the anterior part 
of the rectus is cut away, and the transversalis is exposed. 

1, The median and other nerves of the brachial plexus ; 2, the internal cutaneous ; 3, 



INTERCOSTAL NERVES. 657 

the nerve of Wrisberg; 4, the intercostal nerves continued forwards to 4', their anteiior 
cutaneous twigs ; 5, the lateral cutaneous branches of these nerves ; 6, cutaneous branch 
of the last dorsal spinal nerve ; 7, the iliac twig of the ilio-hypogastric branch of the 
first lumbar nerve ; 8, termination of the ilio-hypogastric ; 9, the ilio-iuguinal ; 10, the 
middle cutaneous of the thigh. 

the sternum, they cross the internal mammary artery and the fibres of the 
triangularis sterni muscle. Finally, these nerves pierce the internal inter- 
costal muscle and the greater pectoral, and end in the integument of the 
breast, receiving the name of the anterior cutaneous nerves of the thorax. 

At the anterior part of the chest some of the muscular twigs cross the cartilages 
of the ribs, passing from one intercostal space to another. 

(a) The lateral cutaneous nerves of the thorax pierce the external intercostal and 
serratus magnus muscles, in a line a little behind the pectoral border of the axilla. 
The first intercostal usually gives no lateral branch or only a slender twig to the 
axilla, but, when that of the second nerve is unusually small, it is supplemented by 
that of the first. The branch from the .second intercostal is named intercosto-humeral, 
and requires separate description. Each of the remaining lateral cutaneous nerves 
divides into two branches, which reach the integument at a short distance from each 
other, and are named anterior and posterior. 

The anterior branches are continued forwards over the border of the great pectoral 
muscle. Several reach the mammary gland and the nipple; and from the lower 
nerves twigs are supplied to the digitations of the external oblique muscle of the 
abdomen. 

The posterior branches turn backwards to the integument over the scapula and the 
latissimus dorsi muscle. The branch from the third nerve ramifies in the axilla, and 
a few filaments reach the arm. 

The intercosto-humeral nerve, the lateral cutaneous branch of the second inter- 
costal nerve, corresponds with the posterior of the two divisions of the succeeding 
lateral cutaneous branches, the anterior being commonly wanting. It crosses the 
axillary space to reach the arm, and is connected in the axilla with an offset of the 
nerve of Wrisberg. Penetrating the fascia, it becomes subcutaneous, and ramifies in 
the integument of the upper half of the arm, on the inner and posterior aspect ; a 
few filaments reach the integument over the scapula. The branches of this nerve 
cross over the internal cutaneous offset of the musculo-spiral, and a communication 
is established between the two nerves. The size of the intercosto-lmmeral nerve, 
and the extent of its distribution, are in the inverse proportion to the size of the 
other cutaneous nerves of the upper arm, especially the nerve of Wrisberg. 

(b] The anterior cutaneous nerves of the thorax, which are the terminal twigs of the 
intercostal nerves, are reflected outwards in the integument over the great pectoral 
muscle. The branch from the second nerve is connected with the supraclavicular 
and the lateral cutaneous nerves; those from the third and fourth nerves are distri- 
buted to the mammary gland. 

LOWER, OR ABDOMINAL INTERCOSTAL NERVES. 

The lower intercostal nerves are continued from the anterior ends of the 
intercostal spaces, between the internal oblique and the transverse muscle of 
the abdomen, to the outer edge of the rectus. Perforating the sheath, 
they enter the substance of that muscle, and afterwards terminate in small 
cutaneous branches (anterior cutaneous). 

(a) The lateral cutaneous nerves of the abdomen pass to the integument through 
the external intercostal and external oblique muscles, in a line with the correspond- 
ing nerves on the thorax, and divide in the same manner into anterior and posterior 
branches. 

The anterior branches are the larger, and are directed inwards in the superficial 
fascia, with small cutaneous arteries, nearly to the edge of the rectus muscle. 
The posterior branches bend backwards over the latissimus dorsi muscle. 

(b) The anterior cutaneous nerves of the abdomen become subcutaneous near the 



658 THE LUMBAR PLEXUS. 

linea alba, accompanying the small perforating arteries. Their number and position 
are very uncertain. They are directed outwards towards the lateral cutaneous nerves. 
A second set is described by Cruveilhier as existing at the outer edge of the rectus 
muscle. 

LAST DORSAL NERVE. 

The anterior primary division of this nerve is below the last rib, and is 
contained altogether in the abdominal wall. The nerve has the general 
course and distribution of the others between the internal oblique and 
transversalis, but, before taking its place between those muscles, it passes in 
front of the upper part of the quadratus lumborum, and pierces the posterior 
aponeurosis of the transverse muscle. This nerve is connected by offsets 
with the nerve above, and occasionally with the ilio-hypogastric branch of 
the lumbar plexus. Near the spine it sometimes communicates with the 
first lumbar nerve by means of a small cord in the substance of the quad- 
ratus lumborum. 

The lateral cutaneous branch of the last dorsal nerve^ passing through both 
oblique muscles, is directed downwards over the iliac crest to the integument, 
covering the fore part of the gluteal region and the upper and outer part of 
the thigh, some filaments reaching as far as the great trochanter of the 
femur. 

ANTERIOR PRIMARY DIVISIONS OF THE LUMBAR NERVES. 

The anterior divisions of the lumbar nerves increase in size from the first 
to the fifth ; and all, except the fifth, which passes down to join the sacral 
nerves, are connected together by communicating loops, so as to form the 
lumbar plexus. On leaving the inter vertebral foramina these nerves are 
connected by filaments with the sympathetic nerve, these filaments being 
longer than those connected with other spinal nerves, in consequence of the 
position of the lumbar sympathetic ganglia on the fore part of the bodies of 
the vertebrse. In the same situation are furnished small twigs to the psoas 
and quadratus lumborum muscles. 

LUMBAR PLEXUS. 

The lumbar plexus is formed by the communications between the anterior 
primary divisions of the four upper lumbar nerves. It is placed in the 
substance of the psoas muscle, in front of the transverse processes of the 
corresponding vertebrae. Above, the plexus is narrow, and is sometimes 
connected with the last dorsal nerve by a small offset from that nerve, 
named dorsi-lumbar ; below it is wider, and is joined to the sacral plexus 
by means of a branch given by the fourth lumbar nerve to the fifth. 

The arrangement of the plexus may be thus stated. The first nerve 
gives off the ilio-hypogastric and ilio-inguinal nerves, and sends downwards 
a communicating branch to the second nerve. The second furnishes the 
greater part of the geuito-crural and external cutaneous nerves, and gives a 
connecting branch to the third, from which some of the fibres of the anterior 
crural and obturator nerves are derived. From the third nerve, besides the 
descending branch to the fourth, two branches proceed : one of these, the 
larger, forms part of the anterior crural nerve ; the other, a part of the 
obturator nerve. The fourth nerve gives two branches, which serve to 
complete the obturator and anterior crural nerves, and a connecting branch 
to the fifth nerve. 



THE LUMBAR PLEXUS AND NEKVES. 



659 



The branches of this plexus form two sets, which are distributed, one to 
the lower part of the wall of the abdomen, the other to the fore part and 
inner side of the lower liinb. In the former set are the ilio-hypogastric and 



Fig. 436. DIAGRAMMATIC 
OUTLINE OF THE LUMBAR 
AND SACRAL PLEXUSES WITH 
THE PRINCIPAL NERVES 

ARISING FROM THEM. 4 



Fig. 436. 



DXIT 




DXII, placed opposite the 
divided roots of the last dorsal 
nerve ; LI to V, opposite the 
roots of the five lumbar nerves : 
the loops uniting the anterior 
primary divisions of these 
nerves together, and the first 
with the twelfth dorsal are 
shown; SI to V, and CI, the 
same in the sacral and coccy- 
geal nerves ; p, placed on some 
of the nerves marks the pos- 
terior primary divisions cut 
short ; p' p, the plexus formed 
by the union of the posterior 
branches of the third, fourth, 
and fifth sacral and the coccy- 
geal nerves ; d, the abdominal 
continuation of the last dorsal 
nerve, from which d' the iliac 
cutaneous branch arises; 1, 1', 
the ilio-hypogastric and ilio- 
inguinal branches of the first 
lumbar nerve ; 2, the genito- 
crural rising by a loop from 
the first and second lumbar; 
2', external cutaneous of the 
thigh rising by a loop from the 
second and third ; ps, branches 
to the psoas muscle along the 
lumbar plexus ; cr, anterior 
crural nerve from the second, 
third, and fourth lumbar; il, 
branches to the iliacus ; ob, 
obturator nerve from the se- 
cond, third and fourth lumbar 
nerves ; ob', accessory obtura- 
tor; IV, V, loop from the 
fourth and fifth lumbar, form- 
ing the lumbo- sacral cord ; 3, 
superior gluteal nerve ; sc, 
sacral plexus ending in the great 
sciatic nerve ; 4, lesser sciatic 
nerve rising from the plexus 
posteriorly; 4', inferior gluteal 
branches ; 5, inferior puden- 
dal ; 5', posterior cutaneous 
of the thigh and leg ; 6, 6, 
branches to the obturator in- 

ternus and gemellus superior ; 6', 6', branches to the gemellus inferior, quadratus and 
hip-joint ; 7, twigs to the pyriformis ; 8, 8, pudic nerve from the first, second, third, and 
fourth sacral ; 9, visceral branches ; 9', twig to the levator ani ; 10, cutaneous from the 
fourth, which passes round the lower border of the gluteus maximus ; 11, coccygeal 
branches. 



IV 



V 



CI 



660 THE LUMBAR PLEXUS. 

ilio-inguinal nerves, and part of the genito-crural ; and to the latter belong 
the remaining part of the genito-crural nerve, the external cutaneous, the 
obturator, and the anterior crural nerves. 

ILIO-HYPOGASTRIC AND ILIO- INGUINAL NERVES. 

These nerves are the upper two branches from the lumbar plexus ; they 
are both derived from the first lumbar nerve, and have a nearly similar 
distribution. They become subcutaneous by passing between the broad 
muscles of the abdomen, and through the outer one, and end in the integu- 
ment of the groin and scrotum in the male, and the labia pudendi in the 
female, as well as in the integument covering the gluteal muscles. The 
extent of distribution of the one is inversely proportional to that of the 
other. 

The ilio-hypogastric nerve, emerging from the upper part of the psoas 
muscle at the outer border, runs obliquely over the quadratus lumborum to 
the iliac crest, and there perforating the transverse muscle of the abdomen, 
gets between that muscle and the internal oblique, and divides into an iliac 
and hypogastric branch. 

(a) The iliac branch pierces the attachment of both oblique muscles, immediately 
above the iliac crest, and is lost in the integument over the gluteal muscles, behind 
the distribution of the lateral cutaneous branch of the last dorsal nerve. 

(b) The hypogastric or abdominal branch passes on between the transverse and 
internal oblique muscles, and is connected with the ilio-inguinal nerve near the iliac 
crest. It then perforates the internal oblique muscle, and, piercing the aponeurosis of 
the external oblique, a little above the superficial inguinal opening, is distributed to 
the skin of the abdomen above the pubes. 

The size of the iliac branch of this nerve varies inversely with that of the lateral 
cutaneous branch of the twelfth dorsal. The hypogastric branch is not unfrequently 
joined with the last dorsal nerve between the muscles, near the crest of the innominate 
bone. 

The ilio-inguinal nerve, smaller than the preceding, supplies the integu- 
ment of the groin. Descending obliquely outwards over the quadratus 
lumborum, it crosses the fibres of the iliacus muscle, being placed lower 
down than the ilio-hypogastric : it then perforates the transverse muscle 
further forwards than the ilio-hypogastric ; communicating with that nerve 
between the abdominal muscles. Then piercing the internal oblique muscle, 
it descends in the inguinal canal, and emerging at the superficial inguinal 
ring, is distributed to the skin upon the groin, as well as to that upon the 
scrotum and penis ia the male, or the labium pudendi in the female, com- 
municating with the inferior pudendal nerve. Tn its progress this nerve 
furnishes branches to the internal oblique muscle. 

The ilio-inguinal nerve occasionally arises from the loop connecting the first and 
second lumbar nerves. It is sometimes small, and ends near the iliac crest by joining 
the ilio-hypogastric nerve ; in that case the last nerve gives off" an inguinal branch 
having a similar course and distribution to the ilio-inguinal nerve, the place of which 
it supplies. 

GENITO-CRURAL NERVE. 

The genito-crural nerve belongs partly to the external genital organs and 
partly to the thigh. It is derived chiefly from the second lumbar nerve, 
but receives also a few fibres from the connecting cord between that and 
the first nerve. The nerve descends obliquely through the psoas muscle, 
and afterwards on its fore part, towards Poupart's ligament, dividing at a 
variable height into an internal or genital, and an external or crural branch. 



GENITO-CRURAL NERVE. 



661 



It often bifurcates close to its origin from the plexus, in which case its two 
branches perforate the psoas muscle in different places. 

(a) The genital branch (external spermatic, Schmidt), lies upon or near the external 
iliac artery, and sends filaments along that vessel ; then perforating the transversalis 
fascia, it passes through the inguinal canal with the spermatic cord, and is lost upon 




Fig. 437. VIEW FROM BEFORE OP TUE ANTERIOR BRANCHES OP THE LUMBAR AND SACRAL 
NERVES WITH THE PLEXUSES (from Sappey, after Hirschfeld and Leveille). | 

1, lumbar cord of the great sympathetic nerve ; 2, 2', anterior primary divisiun of the 
twelfth dorsal nerve ; 3, first lumbar ; 4, 4', ilio-inguinal branch of this nerve ; 5, 5', 
ilio-hypogastric branch ; 6, second lumbar nerve ; 7, 7', genito-crural nerve rising from 
the first and second lumbar ; 8, 8', external cutaneous nerve of the thigh ; 9, third 
lumbar nerve; 10, fourth ; 11, fifth ; 12, lumbo-sacral trunk ; 13, iliac branch of the 
ilio-inguinal; 1 4, its abdominal branch; 15, its genital branch; 16, external cutaneous 
nerve of the right side passing out of the pelvis under Poupart's ligament ; 17, 17, 17, 
cutaneous ramifications of this nerve ; 17', the same nerve exposed on the left side ; 18, 
18', genital branch of the genito-crural ; 19, its crural branch on the right side becoming 
cutaneous ; 19', the same on the left side exposed as it descends in front of the femoral 
artery ; 20, anterior crural nerve ; 21, 21', obturator nerve ; 22, left sciatic plexus ; 23, 
aortic plexus of the sympathetic nerve connected superiorly with the other pre-aorti'c 
plexuses and the lumbar ganglia, and inferiorly with the hypogastric plexus. 



662 THE LUMBAR PLEXUS. 

the cremaster muscle. In the female it accompanies the round ligament of the 
uterus. 

(b) The crural branch (lumbo-inguinal nerve, Schmidt), descends upon the psoas 
muscle beneath Poupart's ligament into the thigh. Immediately below that liga- 
ment, and at the outer side of the femoral artery, it pierces the fascia lata, and 
supplies the skin on the upper part of the thigh, communicating with the middle 
cutaneous branch of the anterior crural nerve. Whilst it is passing beneath Pou- 
part's ligament, some filaments are prolonged from this nerve on the femoral artery. 
It is stated by Schmidt, that when the crural branch of the genito-crural nerve is 
large, and commences near the plexus, he has observed it to give a muscular branch 
to the lower border of the internal oblique and transversalis muscles. 

EXTERNAL CUTANEOUS NERVES. 

This nerve, commencing from the loop formed between the second and 
third lumbar nerves, on emerging from the outer border of the psoas muscle, 
crosses the iliacus muscle below the ilio-inguiual nerve, and passing beneath 
Poupart's ligament, reaches the thigh beneath the anterior superior iliac 
spine, where it divides into an anterior and a posterior branch distributed to 
the integument of the outer side of the hip and thigh. 

(a) The posterior branch perforates the fascia lata, and subdivides into two or 
three others, which turn backwards and supply the skin upon the outer surface of 
the limb, from the upper border of the hip-bone nearly to the middle of the thigh. 
The highest among them are crossed by the cutaneous branches from the last dorsal 
nerve. 

(b) An anterior branch, the continuation of the nerve, is at first contained in a 
sheath or canal formed in the substance of the fascia lata ; but, about four inches 
below Poupart's ligament, it enters the subcutaneous fatty tissue, and is distributed 
along the outer part of the front of the thigh, ending near the knee. The principal 
offsets spring from its outer side. In some cases, this branch reaches quite down to 
the knee, and communicates there with the internal saphenous nerve. 

OBTURATOR NERVE. 

The obturator nerve (internal crural) is distributed to the adductor 
muscles of the thigh, and to the hip and knee-joints. It arises from the 
lumbar plexus by two roots, one from the third and the other from the 
fourth lumbar nerve. Having emerged from the inner border of the psoas 
muscle, opposite to the brim of the pelvis, it runs along the side of the 
pelvic cavity, above the obturator vessels, as far as the opening in the upper 
part of the thyroid foramen, through which it escapes from the pelvis into 
the thigh. Here it immediately divides into an anterior and a posterior 
branch, which are separated from one another by the short adductor 
muscle. 

A. The anterior portion communicates with the accessory obturator 
nerve, when that nerve is present, and descends in front of the adductor 
brevis and behind the pectineus and adductor longus muscles. It gives 
branches as follows. 

(a) An articular branch to the hip-joint arises near the thyroid membrane. 

(b) Muscular branches are given to the gracilis and adductor longus muscles, and 
occasionally also others to the adductor brevis and pectineus. 

(c) The terminal twig turns outwards upon the femoral artery, and surrounds that 
vessel with small filaments. 

(d) An offset at the lower border of the adductor longus communicates beneath 
the fascia with the internal cutaneous branch of the anterior crural nerve, and with a 
branch of the internal saphenous nerve, forming a sort of plexus. 

Occasional cutaneous neroe. In some instances the communicating branch described 



OBTURATOR NERVE. ACCESSORY. 



663 



is larger than usual, and descends along the posterior border of the sartorius to the 
inner side of the knee, where it perforates the fascia, communicates with the internal 
saphenous nerve, and extends down the inner side of the limb, supplying the skin as 
low as the middle of the leg. 



Fig. 438. 



Fig. 438. THE LUMBAR PLEXUS FROM 

BEFORE, WITH THE DISTRIBUTION OP 

SOME OF ITS NI-.RVES (slightly altered 
from Schmidt). | 

cr, the last rib ; J, quadratus lura- 
boruni muscle ; c, oblique and traus- 
verse muscles cut near the crest of the 
ilium and turned down ; d t pubes ; e, 
adductor brevis muscle ; /, pectineus 
dhided and turned outwards ; g, adduc- 
tor lougus; 1, ilio-hypogastric nerve ; 
2, ilio-inguinal ; 3, external cutaneous; 
4, anterior crural ; 5, accessory obtu- 
rator ; 6, obturator united with the ac- 
cessory by a loop round the pubes; 7, 
geuito-crural in two branches cut short 
near their origin ; 8, 8, lumbar portion 
of the gangliated sympathetic cord. 

When this cutaneous branch of the 
obturator nerve is present, the internal 
cutaneous branch of the anterior crural 
nerve is small, the size of the two 
nerves bearing an inverse proportion 
to each other. 



B. The posterior or deep part 
of the obturator nerve, having 
passed through some fibres of the 
external obturator muscle, crosses 
behind the short adductor to the 
fore part of the adductor mag- 
DUS, where it divides into many 
branches, all of which enter those 
muscles, excepting one which is prolonged downwards to the knee-joint. 

(a) The muscular branches supply the external obturator and the great adductor 
muscle, with the short adductor also when this muscle receives no branch from the 
anterior division of the nerve. 

(b) The articular branch for the knee rests at first on the adductor magnus, but 
perforates the lower fibres of that muscle, and thus reaches the upper part of the 
popliteal space. Supported by the popliteal artery, and sending filaments around 
that vessel, the nerve then descends to the back of the knee-joint, and enters the 
articulation through the posterior ligament. (Thomson, " London Med. and Surg. 
Journal," No. xcv.) 

ACCESSORY OBTURATOR NERVE. 

The accespory obturator nerve, a small and inconstant nerve, arising from 
the obturator nerve near its upper end, or separately from the same nerves 
of the plexus, descends along the inner border of the psoas muscle, over the 
pubic bone, and, passing behind the pectineus muscle, ends by dividing into 
several branches. Of these one joins the anterior branch of the obturator 
nerve ; another penetrates the pectineus on the under surface ; whilst a 
third enters the hip-joint with the articular 'artery. 




664 



THE LUMBAR PLEXUS. 



This nerve is sometimes smaller than usual, and ends in filaments which perforate 
the capsule of the hip-joint. When it is altogether wanting, the hip-joint receives 
branches from the obturator nerve. 

Summary. The obturator nerve and accessory obturator give branches to 
the hip and knee joint?, also to the adductor muscles of the thigh, and, in 
some cases, to the pecfcineus. Occasionally a cutaneous branch descends to 
the inner side of the thigh, and to the inner and upper part of the leg. 



Fir. 439. 



ANTERIOR CRURAL NERVE. 

This nerve is the largest branch of the lumbar plexus, and is derived 
piincipally from the third and fourth lumbar nervea, but in part also from 

the second. Emerging from the outer 
border of the psoas muscle, near its lower 
part, it descends into the thigh in the 
groove between that muscle and the iliacus, 
and, therefore, to the outside of the femoral 
blood-vessels. It now becomes flattened 
out and divides into two parts, one of 
which is cutaneous, while the other is dis- 
tributed to muscles. 



Fig. 439. DEEP NERVES OP THE ANTERIOR AND 
INNER PART OF THE THIGH (from Sappey after 
Hirschfeld and Leveille). 

1, anterior crural nerve ; 2, branches given to 
the iliacus muscle ; 3, branch to the lower pa't of 
the psoas ; 4, large musculo-cutaneous branches, 
divided to show the deeper nerves ; 5 and 6, mus- 
cular filaments from the small musculo-cutaneous ; 
7. origin of the cutaneous branches ; 8, communi- 
cating filament of the internal cutaneous nerves ; 
9, branches to the rectus ; 10, branches to the 
vustus externus ; 11, branches to the vastus inter- 
ims ; 12, internal saphenous nerve ; 13, its patellar 
branch; 14, its continuation down the leg ; 15, 
obturator nerve ; 16, branch from the obturator 
nerve to the adductor longus ; 17, branch to the 
adductor brevis ; 1 8, branch to the gracilis ; from 
this a filament is prolonged downwards, to unite 
with the plexus formed by the union of branches 
from the internal cutaneous and internal saphenous 
nerves ; 19, deep branch of the obturator nerve to 
the adductor magnus ; 20, lumbo- sacral trunk ; 21, 
its union with the first sacral nerve ; 22, 22, lum- 
bar and sacral part of the sympathetic nerve ; 23, 
external cutaneous nerve from the lumbar plexus. 



Branches of the trunk. The branches 
given from the anterior crural nerve within 
the abdomen are few and of small size. 

(a) The iliacus receives three or four small branches, which are directed outwards 
from the nerve to the fore part of the muscle. 

(b) The nerve of the femoral artery is a small branch which divides into numerous 
filaments upon the upper part of that vessel. It sometimes arises lower down than 
i' ;nal in the thigh. It may, on the other hand, be found to take origin above the 
ordinary position ; and in this case it proceeds from the middle cutaneous nerve, 




ANTERIOR CRURAL NERVE. 660 

when that branch springs from or near the lumbar plexus. In either case, its ulti- 
mate distribution is the same as that already described. 

Terminal branches. From the principal or terminal divisions of the nerve 
the remaining branches take their rise as follows. 

From the SUPERFICIAL DIVISION cutaneous branches are given to the fore 
part of the thigh, and to the inner side of the leg. They are the middle and 
internal cutaneous nerves, and the internal saphenous nerve. One of the 
muscles, the sartorius, receives its nerves from this group. 

The DEEP BRANCHES supply the muscles on the fore part of the thigh, and 
also the pectineus muscle. The branch to the pectineus, however, some- 
times arises from the superficial part of the trunk. 

A. MUSCULAR BRANCHES. 

The branch to the pectineus muscle crosses inwards behind the femoral vessels, 
and enters the muscle on the anterior aspect. 

The sartorius muscle receives three or four twigs, which arise in common with 
the cutaneous nerves, and reach mostly the upper part of the muscle. 

The rectus muscle receives a distinct branch on its under surface. 

The nerve for the vastus externus, of considerable size, descends with the branches 
of the external circumflex artery towards the lower part of the muscle. It gives oft 
a long slender articular filament, which reaches the knee and penetrates the fibrous 
capsule of the joint. 

Another large nerve divides into two sets of branches, which enter the vastus 
internus and the crureus about the middle of those muscles. The nerve of the vastus 
internus, before penetrating the muscular fasciculi, gives a small branch to the knee- 
joint. This articular nerve passes along the internal intermuscular septum with a 
branch of the anastomotic artery, as far as the inner side of the joint, where it per- 
forates the capsular ligament, and is directed outwards on the synovial membrane 
beneath the ligamentum patellae. 

B. MIDDLE CUTANEOUS NERVE. 

The middle cutaneous nerve either pierces the fascia lata divided into two 
branches about four inches below Po apart' s ligament, or as one trunk which 
soon separates into two branches. These branches descend side by side on the 
fore part of the thigh to the inner side and front of the patella. After or 
before the nerve has become subcutaneous, it communicates with the crural 
branch of the genito-crural nerve, and also with the internal cutaneous. 

This nerve sometimes arises from the anterior crural, high up within the 
abdomen. 

C. INTERNAL CUTANEOUS NERVE. 

The internal cutaneous nerve gives branches to the skin on the inner side 
of the thigh, and the upper part of the leg ; but the extent to which it 
reaches varies with the presence or absence of the " occasional cutaneous" 
branch of the obturator nerve. 

Lying beneath the fascia lata, this nerve descends obliquely over the 
upper part of the femoral artery. It divides either in front of that vessel, 
or at the inner side, into two branches (one anterior, the other internal), 
which pierce the fascia separately. These two branches sometimes arise as 
distinct offsets from the superficial part of the anterior crural nerve. 

The distribution of the internal cutaneous nerve is as follows. 

(a) Branches previous to division. Before dividing into its two ultimate 
branches, this nerve gives off two or three cutaneous twigs, which accompany the 
upper part of the long saphenous vein. The highest of these perforates the fascia 



666 



THE LUMBAR PLEXUS. 



near the saphenous opening, and reaches down to the middle of the thigh. The 
others appear beneath the skin lower down by the side of the vein ; one, larger than 
the rest, passes through the fascia about the middle of the thigh, and extends to the 
knee. In some instances, these small branches spring directly from the anterior crural 
nerve, and they often communicate with each other. 



Fig. 440. Fig. 440. CUTANEOUS NERVES OP THE ANTERIOR 

AND INNER PART OF THE THIGH (from Sappey 
after Hirschfeld and Leveille). | 

1, external cutaneous nerve ; 2, 2, middle cuta- 
neous branch of the anterior crural passing through 
the sartorius muscle and the fascia ; 3, 3, anterior 
division of the internal cutaneous ; 4, filament to 
the sartorius ; 5, inner or posterior division of the 
internal cutaneous ; 6, its superficial branch to the 
inside of the knee after perforating the fascia ; 7, 
deep or communicating branch ; 8, superficial 
branch of the musculo-cutaneous of the crural ; 9, 
patellar branch of the internal saphenous nerve ; 
10, continuation of the saphenous down the leg. 

(b) The anterior branch, descending in a 
straight line to the knee, perforates the fascia 
lata in the lower part of the thigh ; it after- 
wards runs down near the intermuscular septum, 
giving off filaments on each side to the skin, and 
is finally directed over the patella to the outer 
side of the knee. It communicates above the 
joint with a branch of the long saphenous 
nerve ; and sometimes it takes the place of the 
branch usually given by the latter to the inte- 
gument over the patella. 

This branch of the internal cutaneous nerve 
sometimes lies above the fascia in its whole 
length. It occasionally gives off a cutaneous 
filament, which accompanies the long saphenous 
vein, and in some cases it communicates with 
the branch to be next described. 

The inner branch of the internal cutaneous 
nerve, descending along the posterior border of 
the sartorius muscle, perforates the fascia lata 
at the inner side of the knee, and communicates 
by a small branch with the internal saphenous 
nerve, which here descends in front of it. It 
gives some cutaneous filaments to the lower 
part of the thigh on the inner side, and is dis- 
tributed to the skin upon the inner side of the leg. Whilst beneath the fascia, this 
branch of the internal cutaneous nerve joins in an interlacement with offsets of the 
obturator nerve below the middle of the thigh, and with the branch of the saphenous 
nerve nearer the knee. 




D. INTERNAL SAPHEXOUS NERVE. 

The internal or long saphenous nerve is the largest of the cutaneous 
branches of the anterior crural nerve. In some cases it arises in connection 
with one of the deep or muscular brandies. 

This nerve is deeply placed as far as the knee, and is subcutaneous in the 
rest of its course. In the thigh it accompanies the femoral vessels, lying at 
first somewhat to their outer side, but lower down approaching close to 



ANTERIOR CRURAL. FIFTH LUMBAR NERVE. 667 

them, and passing beneath the same aponeurosis. When the vessels pass 
through the opening in the adductor muscle into the popliteal space, the 
saphenous nerve separates from them, and is continued downwards beneath 
the sartorius muscle to the ianer side of the knee ; where, having first 
given off, as it lies near the inner condyle of the femur, a branch which is 
distributed over the front of the patella, it becomes subcutaneous by piercing 
the fascia between the tendons of the sartorius and gracilis muscles. 

The nerve then accompanies the sapheuous vein along the inner side of 
the leg, and passing in front of the ankle is distributed to the inner side of 
the foot. In the leg it is connected with the internal cutaneous nerve. 

The distribution of the branches is as follows. 

(a) A communicating branch is given off about the middle of the thigh to join in 
the interlacement formed beneath the fascia lata by this nerve and branches of the 
obturator and internal cutaneous nerves. After it has left the aponeurotic covering 
of the femoral vessels, the internal saphenous nerve has, in some cases, a further 
connection with one or other of the nerves just referred to. 

(b) The branch to the integument in front of the patella perforates the sartorius 
muscle and the fascia lata ; and, having received a communicating offset from the 
internal cutaneous nerve, spreads out upon the fore part of the knee ; and, by uniting 
with branches of the middle and external cutaneous nerves, forms a plexus plexus 
patellae. 

(c) A branch to the inner ankle is given off in the lower third of the leg, and 
descends along the margin of the tibia. 

(d) Filaments from this nerve enter the tarsal ligaments. 

Summary. The anterior crural nerve is distributed to the skin upon the 
fore part and inner side of the thigh, commencing below the termination of the 
ilio-inguinal and genito-crural nerves. It furnishes also a cutaneous nerve 
to the inner side of the leg and foot. All the muscles on the front and outer 
side of the thigh receive their nerves from the anterior crural, and the pec- 
tineus is also in part supplied by this nerve, and in part by the obturator. 
The tensor muscle of the fascia lata is supplied from a different source, 
viz., the superior gluteal nerve. Lastly, two branches are given from the 
anterior crural nerve to the knee-joint. 

FIFTH LUMBAR NERVE. 

The anterior branch of the fifth lumbar nerve, having received a fasciculus 
from the nerve next above it, descends to join the first sacral nerve, and 
form part of the sacral plexus. The cord resulting from the union of the 
fifth with a part of the fourth nerve, is named the lumbo-sacral nerve. 

SUPERIOR GLUTEAL NERVE. 

Before joining the first sacral nerve the lumbo-sacral cord gives off from 
behind the superior gluteal nerve ; this offset leaves the pelvis through the 
large sacro-sciatic foramen, above the pyriformis muscle, and divides like 
the gluteal artery into two branches, which are distributed chiefly to the 
smaller gluteal muscles and tensor of the fascia lata. 

(a) The upper branch runs with the gluteal artery along the origin of the gluteus 
minimus, and is lost in it and in the gluteus medius. 

(b) The lower branch crosses over the middle of the gluteus minimus, between 
this and the gluteus medius, and supplying filaments to both those muscles, is con- 
tinued forwards, and terminates in the tensor muscle of the fascia lata. 

x x 2 



668 THE SACRAL NERVES. 

ANTERIOR PRIMARY DIVISIONS OF THE SACRAL AND 
COCCYGEAL NERVES. 

THE SACRAL NERVES. 

The anterior divisions of the first four sacral nerves emerge from the 
spinal canal by the anterior sacral foramina, and the fifth passes out between 
the sacrum and coccyx. 

The first two sacral nerves are large, and of nearly equal size ; the others 
diminish rapidly, and the fifth is exceedingly slender. Like the anterior 
divisions of the other spinal nerves, those of the sacral nerves communicate 
with the sympathetic : the communicating cords are very short, as the 
sympathetic ganglia are close to the inner margin of the foramina of the 
sacrum. 

The first three nerves and part of the fourth contribute to form the sacral 
plexus. The fifth has no share in the plexus, it ends on the back of the 
coccyx. As the description of the fourth and fifth sacral nerves and of the 
coccygeal will occupy only a short space, these three nerves may be noticed 
first, before the other nerves and the numerous branches to which they 
give rise are described. 

THE FOURTH SACRAL NERVE. 

Only one part of the anterior division of this nerve joins the sacral 
plexus ; the remainder, which is nearly half the nerve, supplies branches to 
the viscera and muscles of the pelvis, and sends downwards a connecting 
filament to the fifth nerve. 

(a) The visceral [branches of the fourth sacral nerve are directed forwards to the 
lower part of the bladder, and communicate freely with branches from the sympa- 
thetic nerve. Offsets are distributed to the neighbouring viscera, according to the 
sex. They will be described with the pelvic portion of the sympathetic nerve. The 
foregoing branches are, in some instances, furnished by the third sacral nerve instead 
of the fourth, and not unfrequently from both of these nerves. 

(b) Of the muscular branches, one supplies the levator ani, piercing that muscle 
on the pelvic surface ; another enters the coccygeus, whilst a third ends in the external 
sphincter muscle of the rectum. The last branch, after passing either through the 
coccygeus, or between it and the levator ani, reaches the perinaeum, and is distributed 
likewise to the integuments between the anus and the coccyx. 

THE FIFTH SACRAL NERVE. 

The anterior branch of this, the lowest sacral nerve, comes forwards 
through the coccygeus muscle opposite the junction of the sacrum with the 
first coccygeal vertebra ; it then descends upon the coccygeus nearly to the 
tip of the coccyx, where it turns backwards through the fibres of that 
muscle, and ends in the integument upon the posterior and lateral aspect of 
the bone. 

As soon as this nerve appears in front of the bone (in the pelvis) it is joined 
by the descending filament from the fourth nerve, and lower down by the small 
anterior division of the coccygeal nerve. It supplies small filaments to the coccygeus 
muscle. 

THE COCCYGEAL NERVE. 

The anterior branch of the coccygeal, or, as it is sometimes named, the 
sixth sacral nerve, is a very small filament. It escapes from the spinal 



THE SACRAL PLEXUS. 



669 



canal by the terminal opening, pierces the sacro-sciatic ligament and the 
coccygeus muscle, and, being joined upon the side of the coccyx with the 
fifth sacral nerve, partakes in the distribution of that nerve. 

THE SACRAL PLEXUS. 

The lumbo-sacral cord (resulting as before described from the junction of 



Fig. 441. 



Fig. 441. DIAGRAMMATIC 
OUTLINE OP THE LUMBAR 
AND SACRAL PLEXUSES WITH 
THE PRINCIPAL NERYKS 

ARISING FROM THEM. ^ 

The references to the nerves 
of the lumbar plexus will be 
found at p. 659. DXII, 
roots of the last dorsal nerve ; 
LI to V, roots of the five 
lumbar nerves ; SI to V, and 
CI, roots of the five sacral 
and the coccygeal nerves ; 
IV, V, loop from the an- 
terior primary branches of 
the fourth and fifth lumbar 
nerves, forming the lumbo- 
sacral cord ; 3, superior glu- 
teal nerve ; SO, sacral plexus 
ending in the great sciatic 
nerve ; 4, lesser sciatic nerve, 
rising from the plexus pos- 
teriorly ; 4', inferior gluteal 
branches ; 5, inferior puden- 
dal ; 5', posterior cutaneous 
of the thigh and leg ; 6, 6, 
branches to the obturator in- 
ternus and gemellus superior ; 
6', 6', branches to the ge- 
inellus inferior, quadratus and 
hip-joint ; 7, twigs to the 
pyriformis ; 8, 8, pudic from 
the first, second, third, and 
fourth sacral ; 9, visceral 
branches ; 9', twig to the 
levator ani ; 10, cutaneous 
from the fourth, which passes 
round the lower border of the 
gluteus maximus; 11, coccy- 
geal branches. 



the fifth and part of the 
fourth lumbar nerves), 
the anterior divisions 
of the first three sacral 
nerves, and part of the 
fourth, unite to form 
this plexus. Its con- 
struction differs from 
that of the other spi- 
nal nervous plexuses 
in this respest, that the several constituent nerves entering into it 




ci 



670 THE SACRAL PLEXUS. 

unite into one broad flat cord. To the place of union the nerves proceed in 
different directions, that of the upper ones being obliquely downwards, while 
that of the lower is nearly horizontal ; and, as a consequence of this 
difference, they diminish in length from the first to the last. The sacral 
plexus rests on the anterior surface of the pyriform muscle, opposite the side 
of the sacrum, and escaping through the great sacro-sciatic foramen, ends in 
the great sciatic nerve. 

Branches. The sacral plexus gives rise to the great sciatic nerve, and to 
various smaller branches ; viz., the pudic nerve, the small sciatic nerve, and 
branches to the obturator internus, pyriformis, gemelli, and quadratus 
femoris muscles. 

MUSCULAR BRANCHES. 

a. To the pyriformis muscle, one or more branches are given, either from the plexus 
or from the upper sacral nerves before they reach the plexus. 

b. The nerve of the internal obturator muscle arises from the part of the plexus 
formed by the union of the lumbo-sacral and the first sacral nerves. It turns over 
the ischial spine of the hip-bone with the pudic vessels, and is then directed forwards 
through the small sacro-sciatic foramen to reach the inner surface of the obturator 
muscle. 

c. To the levator ani one or more twigs proceed from the lower part of the plexus. 

d. The superior gemellus receives a small branch, which arises from the lower part 
of the plexus. 

e. The small nerve which supplies the lower gemellus and quadratus femoris 
muscles springs from the lower part of the plexus. Concealed at first by the great 
sciatic nerve, it passes beneath the gemelli and the tendon of the internal obturator, 
between those muscles and the capsule of the hip-joint, and reaches the deep 
(anterior) surface of the quadratus. It furnishes a small articular filament to the 
back part of the hip-joint. 

THE PUDIC NERVE. 

This nerve, arising from the lower part of the sacral plexus, turns over 
the spine of the ischium, and then passes forwards through the small sacro- 
sciatic foramen, where it usually gives off the inferior hsemorrhoidal branch. 
It is next directed along the outer part of the ischio-rectal fossa, in a sheath 
of the obturator fascia, along with the pudic vessels, and divides into two 
terminal branches, the perinseal nerve and the dorsal nerve of the penis. 

A. The perinceal nerve, the lower and much the larger of the two 
divisions of the pudic nerve, lies below the pudic artery, and is expended in 
superficial and muscular branches. 

a. The superficial perinceal branches are two in number, anterior and posterior. 
The posterior branch, which first separates from the perinseal nerve, reaching the back 
part of the ischio-rectal fossa, gives filaments inwards to the skin in front of the 
anus, and turns forwards in company with the anterior branch to reach the scrotum. 
The anterior branch descends to the fore part of the ischio-rectal fossa ; and, passing 
forwaids with the superficial perinaeal artery, ramifies in the skin on the fore part of 
the scrotum and on the penis. This branch sends small twigs to the levator ani 
muscle. The superficial perinseal nerves are accompanied to the scrotum by the 
inferior pudendal branch of the small sciatic nerve. The three branches are some- 
times named long ncrotal nerves. 

In the female, both the superficial perinaeal branches terminate in the external 
labium pudendi. 

b. The muscular branches generally arise by a single trunk, which is directed 
inwards under cover of the transversalis perinaei muscle, and divides into offsets which 



PUDIC XEEYE. 



671 



are distributed to the tranversalis perinaei, erector penis, accelerator urinae, and 
compressor urethras. 



c. Slender filaments are sent inwards to the corpus spongiosum urethras ; some of 
these, before penetrating the erectile tissue, run a considerable distance over its 
surface. 



Fig. 442. RIGHT SIPE OF THE Fig. 442. 

INTERIOR OP THE MALE PELVIS, 
WITH THE PRINCIPAL NERVKS 
DISPLAYED (from Hirschfeld and 
Leveille). 

The left wall has been removed 
as far as the sacrum behind and 
the sympbysis pubis in front; the 
viscera and the lower part of the 
levator ani have been removed ; 
a, the lower part of the aorta ; a', 
placed on the fifth lumbar ver- 
tebra, between the two common 
iliac arteries, of which the left is 
cut short ; b, the right external 
iliac artery and vein ; c, the sym- 
physis pubis ; d, the divided py- 
riformis muscle, close to the left 
auricular surface of the sacrum ; 
e, bulb of the urethra covered by 
the accelerator urinas muscle ; the 
membranous part of the urethra 
cut short is seen passing into it ; 
1, placed on the crest of the ilium, 
points to the external cutaneous 
nerve of the thigh passing over 
the iliacus muscle ; 2, placed on 
the psoas muscle, points to the 
genito-crural nerve ; 3, obturator nerve ; 4, 4, placed on the lumbo-sacral cords ; that of 
the right side points to the gluteal artery cut short ; 4', the superior gluteal nerve ; 5, 
placed on the inside of the right sacral plexus, points by four lines to the anterior divisions 
of the four upper sacral nerves, which, with the lumbo-sacral cord, unite in the plexus ; 
5', placed on the fifth piece of the sacrum, points to the fifth sacral nerves ; 5", the 
visceral branches proceeding from the third and fourth sacral nerves ; 6, placed on the 
lower part of the coccyx, below the coccygeal nerves ; 7, placed on the line of division of 
the pelvic fascia, points to the nerve of the levator ani muscle ; 8, placed at the lower 
border of the great sacro-sciatic ligament, points to the cutaneous nerves of the anus ; 9, 
nerve of the obturator internus ; 10, the pudic nerve; 10', is placed above the muscular 
branches of the perineal nerve ; 10", the anterior and posterior superficial perineal nerves, 
and on the scrotum the distribution of these nerves and the inferior pudendal nerve ; 11, 
the right dorsal nerve of the penis; IT, the nerve on the left crus penis which is cut 
short ; 12, the continuation of the lesser sciatic nerve on the back of the thigh ; 12', the 
inferior pudendal branch ; 13, placed on the transverse process of the fifth lumbar ver- 
tebra, marks the lowest lumbar sympathetic ganglion ; 14, placed on the body of the first 
piece of the sacrum, points to the upper sacral sympathetic ganglia ; between 14 and 6, 
are seen the remaining ganglia and sympathetic nervous cords, as well as their union with 
the sacral and coccygeal nerves, and at 6, the lowest ganglion or ganglion impar. 




B. The dorsal nerve of the penis, the upper division of the pudic nerve, 
accompanies the pudic artery in its course between the layers of the deep 
perinseal or subptibic fascia, and afterwards through the suspensory 
ligament, to reach the dorsum of the penis, along which it passes as far as 
the glands, where it divides into filaments for the supply of that part. On 



672 THE SACRAL PLEXUS. 

the penis, this nerve is joined by branches of the sympathetic system, and 
it sends outwards numerous offsets to the integument on the upper surface 
and sides of the organ, including the prepuce. One large branch penetrates 
the corpus cavernosum penis. 

In the female, the dorsal nerve of the clitoris is much smaller than the 
corresponding branch in the male ; it is similarly distributed. 

C. The inferior hcemorrhoidal nerve arises from the pudic nerve at the 
back of the pelvis, or it may come directly from the sacral plexus, and be 
transmitted through the small sacro-sciatic foramen to its distribution in the 
lower end of the rectum. 

Fig. 443. 




Fig. 443. DISSECTION OF THE PERINEUM OP THE MALE TO SHOW THE DISTRIBUTION OP 
THE PUDIO AND OTHER NERVES (from Hirschfeld and Leveille). ^ 

On the right side a part of the glutens maximus muscle and the great sacro-sciatic liga- 
ment have been removed to show the descent of the nerves from the great sacro-sciatic 
foramen. 1, great sciatic nerve of the right side ; 2, lesser sciatic nerve ; 2', its muscular 
branches to the gluteus maximus (right side) ; 2", cutaneous branches to the buttock (left 
side) ; 3, continuation of the nerve as posterior middle cutaneous of the thigh ; 3, internal 
and external cutaneous branches ; 4, 4, inferior pudendal branch ; 4', network of this and 
the perineal nerves on the scrotum ; 5, right pudic nerve ; 6, superior branch or nerve 
to the penis ; 7, the external superficial perineal branch ; 7', the internal superficial 
perineal branch ; 8, musculo-bulbal branches ; 9, hemorrhoidal or cutaneous anal branches ; 
1.0, cutaneous branch of the fourth sacral nerve. 

Some of the branches of this nerve end in the external sphincter and in the adjacent 
skin of the anus ; others reach the skin in front of that part, and communicate with 
the inferior pudendal branch of the small sciatic nerve, and with the superficial 
perineal nerves. 

Summary. The pudic nerve supplies the perinsBiim, the penis, and part 
of the scrotum, also the urethral and anal muscles in the male ; and the 



SMALL SCIATIC NERYE. 



673 



clitoris, labia, and other corresponding parts in the female. It communicates 
with the inferior pudendal branch of the small sciatic nerve. 

SMALL SCIATIC NERVE. 

The small sciatic nerve (tiervus ischiadicus minor) is chiefly a cutaneous 
nerve, supplying the integument of the lower part of the buttock, the back 
of the thigh, and upper part of the calf of the leg; it furnishes also branches 
to one muscle the gluteus maximus. 

This nerve is formed by the union of two or more nervous cords, derived 
from the lower and back part of the sacral plexus. Arising below the pyriform 
muscle, it descends beneath the gluteus maximus, and at the lower border 
of that muscle comes into contact with the fascia lata. Continuing its 
course downwards along the back of the limb, it perforates the fascia a 
little below the knee. 



Fig. 444. DEEP NERVES IN THE 
GLUTEAL AND INFERIOR PUDENDAL 
REGIONS (from Hirschfeld and Le- 
veille). \ 



Fig. 441. 




, back part of the great trochanter ; 
b, tensor vaginae feraoris muscle ; c t 
tendon of the obturator internus muscle 
near its insertion ; d, upper part of the 
vastus externus ; e, coccyx ; f t gracilis 
muscle ; between /"and cl, the adductor 
magnus, semitendinosus, and biceps 
muscles ; * placed at the meeting of the 
crura penis above the urethia ; 1, 
placed upon the ilium close above the 
sacro-sciatic notch, marks the superior 
gluteal nerve, and on the divided parts 
of the gluteus meclius muscle, the supe- 
rior branch of the nerve ; 1', on the 
surface of the gluteus minimus muscle, 
the inferior branch of the nerve ; 1", 
branch of the nerve to the tensor vaginae 
fernoris ; 2, sacral plexus and great 
sciatic nerve ; 2', muscular twig from 
the plexus to the pyriformis ; 2", mus- 
cular branches to the geraellus superior 
and obturator internus ; 3, lesser sciatic 
nerve ; 3', placed on the upper and 
lower parts of the divided gluteus 

maximus, the inferior gluteal muscular branches of the lesser sciatic nerve ; 3", the 
cutaneous branches of the same nerve winding round the lower border of the gluteus 
maximus ; 4, the continuation of the lesser sciatic nerve as posterior cutaneous nerve of 
the thigh ; 4', inferior pudendal branch of the lesser sciatic ; 5, placed on the lower part 
of the sacral plexus, points to the origin of the pudic nerve ; 6, its perineal division with, 
its muscular branches ; b', anterior or superior superficial perineal branch ; 6", posterior 
or inferior superficial perineal ; + + , distribution of these nerves and the inferior puden- 
dal on the scrotum ; 7, dorsal nerve of the penis. 

The branches of tho small sciatic nerve are as follows. 

A. The inferior gluteal branches, given off under the gluteus maximus, supply the 
lower part of that muscle. A distinct gluteal branch commonly proceeds from the 
sacral plexus to the upper part of the muscle. 

B. The cutaneous branches of the nerve principally emerge from beneath the lower 
border of the gluteus maximus, arranged iu an external and an internal set. Others 
appear lower down. 



674 



NERVES OF THE LOWER LIMB. 



a. The internal are mostly distributed to the skin of the inner side of the thigh 
at the upper part. One branch, however, which is much larger than the rest, is 
distinguished as the inferior pudendal. 

Fig. 445. 





Fig. 445. POSTERIOR CUTANEOUS NERVES OF THE HIP AND THIGH 
(from Hirschfeld and Leveille). 

F a, gluteus maxinms muscle partially uncovered by the removal of a part of the fascia 
lata, and divided at its inferior part to show the lesser sciatic nerve ; b, fascia lata over 
the glutei muscles and the outer part of the hip ; c, d, part of the semitendinosus, biceps, 
and semimembranosus muscles exposed by the removal of the fascia ; e, gastrocnemius ; 
/, coccyx ; g, internal branches of the saphena vein ; 1, iliac cutaneous branches of the 
ilio-inguinal and ilio-hypogastric nerves ; 2, cutaneous iliac branches of the last inter- 
costal ; 3, posterior twigs of the external cutaneous nerve of the thigh ; 4, lesser sciatic 
nerve issuing from below the gluteus maximus muscle ; 4', its muscular branches ; 
4", its cutaneous gluteal branches ; 5, posterior middle cutaneous continued from 
the lesser sciatic ; 5', 5', its inner and outer branches spreading on the fascia of the 
thigh ; 6, 6, its terminal branches descending on the calf of the leg ; 7, posterior tibial 
and fibular nerves separating in the popliteal space ; 8, lower posterior divisions of the 
sacral and coccygeal nerves ; 9, inferior pudendal nerve. 

Fig. 446. DEEP POSTERIOR NERVES OF THE HIP AND THIGH 
(from Hirschfeld and Leveilie). | 

, gluteus medius muscle ; I, gluteus maximus ; c, pyriformis ; d, placed on the 



GREAT SCIATIC NERVE. 675 

trochanter major, points to the tendon of the obturator internus ; e, upper part of the 
femoral head of the biceps; f, semitendinosus ; g, semimembranosus ; h, gastrocnemins ; 
i, popliteal artery; 1, placed on the gluteus minimus muscle, points to the superior 
gluteal nerves ; 2, inferior gluteal branches of the lesser sciatic; 3, placed on the greater 
sacro- sciatic ligament, points to the pudic nerve ; 3', its farther course ; 4, inferior 
pudendal ; 5, placed on the upper divided part of the semitendinosus and biceps, points 
to the posterior middle cutaneous nerve of the thigh ; 6, great sciatic nerve, 6', 6', some 
of its muscular branches to the flexors ; 7, internal popliteal or posterior tibial nerve ; 7', 
its muscular or sural branches ; 8, external popliteal or peroneal nerve ; 8', its external 
cutaneous branch ; 9, communicating tibial ; &', communicating peroneal branch to the 
external saphenous nerve. 

The inferior pudendal branch turns forwards below the ischial tuberosity to reach 
the perinseum. Its filaments then extend forwards to the front and outer part of the 
scrotum, and communicate with one of the superficial perineal nerves. In the female, 
the inferior pudendal branch is distributed to the external labium pudendi. 

b. The external cutaneous branches, two or three in number, turn upwards in a 
retrograde course to the skin over the lower and outer part of the great gluteal 
muscle. In some instances one takes a different course, descending and ramifying 
in the integuments on the outer side of the thigh nearly to the middle. 

c. Of the lower branches some small cutaneous filaments pierce the fascia of the 
thigh above the popliteal space. One of these, arising somewhat above t'he knee-joint, 
is prolonged over the popliteal region to the upper part of the leg. 

Of the terminal twigs, perforating the fascia lata opposite the lower part of the 
popliteal space, one accompanies the short saphenous vein beyond the middle of the 
leg, and others pass into the integument covering the inner and outer heads of the 
gastrocnemius muscle. Its terminal cutaneous branches communicate with the short 
saphenous nerve. 

GREAT SCIATIC NERVE. 

The great sciatic nerve (nervus ischiadicus), the largest nerve in the body, 
supplies the muscles at the back of the thigh, and by its branches of con- 
tinuation gives nerves to all the muscles below the knee and to the greater 
part of the integument of the leg and foot. The several joints of the 
lower limb receive filaments from it and its branches. 

This large nerve is continued from the lower end of the sacral plexus. It 
escapes from the pelvis through the great sacro-sciatic foramen, below the pyri- 
formis muscle, and reaches down below the middle of the thigh, where it 
separates into two large divisions, named the internal and external popliteal 
nerves. At first it lies in the hollow between the great trochauter and the 
ischial tuberosity, covered by the gluteus maximus and resting on the 
gemelli, obturator internus and quadratus femoria muscles, in company with 
the small sciatic nerve and the sciatic artery, and receiving from that artery a 
branch which runs for some distance in its substance. Lower down it rests 
on the adductor magnus, and is covered behind by the long head of the 
biceps muscle. 

The bifurcation of the sciatic nerve may take place at any point intermediate 
between the sacral plexus and the lower part of the thigh ; and, occasionally, it is 
found to occur even within the pelvis, a portion of the pyriformis muscle being inter- 
posed between the two great divisions of the nerve. 

Branches of the trunk. In its course downwards, the great sciatic nerve 
supplies offsets to some contiguous parts, viz., to the hip-joint, and to the 
muscles at the back of the thigh. 

a. The articular branches are derived from the upper end of the nerve, and enter 
the capsular ligament of the hip-joint, on the posterior aspect. They sometimes arise 
from the sacral plexus. 



676 



XERVES OF THE LOWER LIMB. 



6. The muscular branches are given off under cover of the biceps muscle ; they 
supply the flexors of the leg, viz., the biceps, semitendinosug, and semimembranosus. 
A branch is likewise given to the adductor magnus. t 

TNTERNAL POPLITEAL NERVE. 

The internal popliteal nerve, the larger of the two divisions of the great 
sciatic nerve, following the same direction as the parent trunk, continues 
along the middle of the popliteal space to the lower border of the popliteus 
muscle, beneath which point the continuation of the trunk receives the 
name of posterior tibial. The interior popliteal nerve lies at first at a 
considerable distance from the popliteal artery, 
Fig. 447. at the outer side and nearer to the surface ; but, 

from the knee-joint downwards, the nerve, 
continuing a straight course, is close behind 
the artery, and then crosses it rather to the 
inner side. 

Fig. 447. POSTERIOR CUTANEOUS NERVES OF THE LEG 
(from Sappey after Hirschfeld and Leveille). 

1, internal popliteal division of the great seiatic nerve ; 
2, branch to the internal part of the gastrocnemius 
muscle ; 3, 4, branches to the external part and plan- 
taris ; 5, communicating branch to the external saphe- 
neous nerve ; 6, external popliteal nerve ; 7, cutaneous 
branch ; 8, communicating branch descending to unite 
with that from the internal popliteal in, 9, the external 
saphenous nerve ; 10, calcaneal branch from this nerve ; 
11, calcaneal and plantar cutaneous branches from the 
posterior tibial nerve; 12, internal saphenous nerve; 
13, posterior branches of this nerve. 

The inner division of the sciatic nerve, from its 
commencement to its partition at the foot, is often 
described in anatomical works under the same appel- 
lation throughout ; the name varying, however, with 
different writers, as for example, " cruralis internus," 
or " popliteus internus," Winslow : " tibialis pos- 
terior," Haller : " tibialis vel tibieus," Fischer, &c. 

Branches. The internal popliteal nerve sup- 
plies branches to the knee-joint and to the 
muscles of the calf of the leg, and also part of 
a cutaneous branch, the external or short sa- 
phenous nerve. 

ARTICULAR SERVES. The articular branches are 
generally three in number ; two of these accompany 
the upper and lower articular arteries of the inner 
side of the knee-joint, the third follows the middle 

or azygos artery. These nerves pierce the ligamentous tissue of the joint. The 

upper one is often wanting. 

MUSCULAR BRANCHES. The muscular branches of the internal popliteal 
nerve arise behind the knee-joint, while the nerve is between the heads of 
the gastrocnemius muscle. 

a. The nerves to the gastrocnemius consist of two branches, which separate, one 
to supply each part of the muscle. 




POSTERIOR TIBIAL NERVE. 677 

b. The small nerve of the idantaris muscle is derived from the outer of the branches 
just described, or directly from the main trunk (internal popliteal). 

c. The soleus receives a branch of considerable size, which enters the muscle on the 
posterior aspect after descending to it in front of the gastrocnemius. 

d. The nerve of the popliteus muscle lies deeper than the preceding branches, and 
arises somewhat below the joint ; it descends along the outer side of the popliteal 
vessels, and, after turning beneath the lower border of the muscle, enters the deep or 
anterior surface. 

EXTERNAL OE SHORT SAPHENOUS NERVE. 

The cutaneous branch of the internal popliteal nerve (ramus communicans 
tibialia) descends along the leg beneath the fascia, resting on the gastro- 
cnemius, in the furrow between the heads of the muscle, to about midway 
between the knee and the foot. Here it perforates the fascia, and a little 
lower down is usually joined by a branch from the external popliteal nerve 
(communicans peronei). After receiving this communicating branch, the 
external saphenous nerve descends beneath the integument near the outer 
side of the tendo Achillis in company with the short saphenous vein, and 
turns forwards beneath the outer malleolus to end in the skin at the side of 
the foot and on the little toe. On the dorsum of the. foot this nerve com- 
municates with the musculo- cutaneous nerve. 

In many cases, the external saphenous nerve supplies the outer side of the fourth 
toe, as well as the little toe. The union between the saphenous nerve and the branch 
cf the external popliteal nerve occurs in some cases higher than usual, occasionally even 
at or close to the popliteal space. It sometimes happens that the communication 
between the nerves is altogether wanting ; in which case the cutaneous nerve to the 
foot is generally continued from the branch of the internal popliteal nerve. 

POSTERIOR TIBIAL NERVE. 

The internal popliteal nerve receives the name of posterior tibial at the 
lower margin of the popliteus muscle. It passes down the leg with the pos- 
terior tibial artery, lying for a short distance at the inner side of the vessel, 
and afterwards at the outer side ; the artery inclining inwards from its origin 
while the nerve continues its straight course. In the interval between the 
inner malleolus and the heel, it divides into the two plantar nerves (internal 
and external). The posterior tibial nerve, like the accompanying vessels, is 
covered at first by the muscles of the calf of the leg, afterwards only by 
the integument and fascia, and it rests upon the deep-seated muscles. 

Lateral branches. The deep muscles on the back of the leg and the 
integument of the sole of the foot receive branches from the posterior tibial 
nerve in its course along the leg. 

a. The muscular branches emanate from the upper part of the nerve, either sepa- 
rately or by a common trunk ; and one is distributed to each of the deep muscles, 
viz., the tibialis posticus, the long flexor of the toes, and the long flexor of the great 
toe. The branch which supplies the last-named muscle runs along the peroneal 
artery before penetrating the muscle. 

b. A calcaneo-plantar cutaneous branch is furnished from the posterior tibial nerve ; 
the plantar part perforates the internal annular ligament, and ramifies in the integu- 
ment at the inner side of the sole of the foot, and beneath the heel. 

INTERNAL PLANTAR NERVE. 

The internal plantar, the larger of the two nerves to the sole of the foot, 
into which the posterior tibial divides, accompanies the internal or smaller 
plantar artery, and supplies nerves to both sides of the three inner toes, and 
to one side of the fourth. From the point at which it separates from the 



678 



NERVES OF THE LOWER LIMB. 



posterior tibial nerve, it is directed forwards under cover of the first part of 
the abductor of the great toe, and, passing between that muscle and the 
short flexor of the toes, it gives off the internal cutaneous branch for the 
great toe, and divides opposite the middle of the foot into three digital 
branches. The outermost of these branches communicates with the external 
plantar nerve. 

Brandies. a. Small muscular branches are supplied to the abductor pollicis and 
flexor brevis digitorum. 

b. Small plantar cutaneous branches perforate the plantar fascia to ramify in the 
integument of the sole of the foot. 

c. The digital branches are named numerically from within outwards : the three 
outer pass from under cover of the plantar fascia near the clefts between the toes. 
The first or innermost branch continues single, but the other three bifurcate to supply 
the adjacent sides of two toes. These branches require separate notice. 

The first digital branch is that destined for the inner side of the great toe ; it 
becomes subcutaneous farther back than the others, and sends off a branch to the 
flexor brevis pollicis. 



Fi ? . 448. 




Fig. 448. SUPERFICIAL AND DEEP DISTRIBUTION OP 
THE PLANTAR NERVES (from Hirschf'eld and Le- 
veille, slightly modified). J 



The flexor communis brevis, the abductor pollicis 
and abductor minimi digiti, a part of the tendons 
of the flexor communis longus, together with the lum- 
bricales muscles, have been removed so as to bring 
into view the trans versus and interossei in the middle 
of the foot. 

a, upon the posterior extremity of the flexor com- 
munis brevis, near which, descending over the heel, 
are seen ramifications of the calcaneal branch of 
the posterior tibial nerve ; b, abductor pollicis ; c, 
tendon of the flexor communis longus divided close to 
the place where it is joined by the flexor accessorius ; 
d, abductor minimi digiti ; e, tendon of the flexor 
longus pollicis between the two portions of the flexor 
brevis pollicis ; 1, internal plantar nerve giving some 
twigs to the abductor pollicis, and 1', a branch to the 
flexor communis brevis, cut as it lies on the acces- 
sorius ; 2, inner branch of the internal plantar nerve 
giving branches to the abductor pollicis, flexor brevis 
pollicis, and forming, 2', the internal cutaneous of 
the great toe ; 3, continuation of the internal plantar 
nerve, dividing subsequently into three branches, 
which form, 3', 3', 3', the collateral plantar cutaneous 
nerves of the first and second, second and third, and 
third and fourth toes ; 4, the external plantar nerve ; 
4', its branch to the abductor minimi digiti ; 5, twig 
of union between the plantar nerves ; 6, superficial 
branch of the external plantar nerve ; subsequently 
dividing into 6', 6', the collateral cutaneous nerves of 

the fourth and fifth toes and the external nerve of the fifth ; 7, deep branch of the 
external plantar nerve giving twigs to the adductor pollicis, the interossei, the trans- 
versalis, and to the third and fourth lumbricales muscles. 

The second branch having reached the interval between the first and second meta- 
tarsal bones, furnishes a small twig to the first lumbricalis muscle, and bifurcates 
behind the cleft between the great toe and the second to supply their contiguous 



The third digital branch, corresponding with the second interosseous space, gives 
a slender filament to the second lumbricalis muscle, and divides in a manner similar 



PLANTAR NERVES. PEROKEAL NERVE. 679 

to that of the second branch into two offsets for the sides of the second and third 
toes. 

The fourth digital branch distributed to the adjacent sides of the third and fourth 
toes, receives a communicating branch from the external plantar nerve. 

Along the sides of the toes, cutaneous and articular filaments are given from these 
digital nerves ; and, opposite the ungual phalanx, each sends a dorsal branch to the 
pulp beneath the nail, and then runs onto the ball of the toe, where it is distributed 
like the nerves of the fingers. 

EXTERNAL PLANTAR NERVE. 

The external plantar nerve completes the supply of digital nerves to the 
toes, furnishing branches to the little toe and half the fourth : it also gives a 
deep branch of considerable size, which is distributed to several of the short 
muscles in the sole of the foot. There is thus a great resemblance 
between the distribution of this nerve in the foot and that of the ulnar 
nerve in the hand. 

The external plantar nerve runs obliquely forwards towards the outer side 
of the foot, along with the external plantar artery, between the flexor brevis 
digitorum and the flexor accessorius, as far as the interval between the 
former muscle and the abductor of the little toe. Here it divides into a 
superficial and a deep branch, having previously furnished offsets to the 
flexor accessorius and the abductor minimi diyiti. 

a. The superficial portion separates into two digital branches, which have the same 
general arrangement as the digital branches of the internal plantar nerve. They are 
distributed thus. 

Digital branches. One of the digital branches continues undivided, and runs 
along the outer side of the little toe : it is smaller than the other, and pierces 
the plantar fascia further back. The short flexor muscle of the little toe, and occa- 
sionally one or two interosseous muscles of the fourth metatarsal space receive 
branches from this nerve. 

The larger digital branch communicates with an offset from the internal plantar 
nerve, and bifurcates near the cleft between the fourth and fifth toes to supply one 
side of each. 

&. The deep or muscular branch of the external plantar nerve dips into the sole of 
the foot with the external plantar artery, under cover of the tendons of the flexor 
muscles and the adductor pollicis, and terminates in numerous branches for the fol- 
lowing muscles : all the interossei (dorsal and plantar) except occasionally one or 
both of those in the fourth space, the two outer lumbricales, the adductor pollicis, 
and the transversalis pedis. 

Summary of the internal popliteal nerve. This nerve supplies all the 
muscles of the back of the leg and sole of the foot, and the integument of 
the plantar aspect of the toes, the sole of the foot, and in part that of the leg. 

EXTERNAL POPLITEAL OR PERONEAL NERVE. 

This nerve descends obliquely along the outer side of the popliteal space, 
lying close to the biceps muscle. Continuing downwards over the outer 
part of the gastrocnemius muscle (between it and the biceps) below the head 
of the fibula, the nerve turns round that bone, passing between it and the 
peroneus longus muscle, and then divides into the anterior tibial and the 
musculo- cutaneous nerves. 

Lateral branches. Some articular and cutaneous branches are derived 
from the external popliteal nerve before its final division. 

ARTICULAR NERVES. The articular branches are conducted to the outer 
side of the capsular ligament of the knee-joint by the upper and lower 



680 



NERVES OF THE LOWER LIMB. 



articular arteries of that side. They sometimes arise together, and the 
upper one occasionally springs from the great sciatic nerve before the bifur- 
cation. 

From the place of division of the external popliteal nerve, a recurrent 
articular nerve ascends through the tibialis anticus muscle with the recur- 
rent artery to reach the fore part of the knee-joint. 

Fig. 449. Fig. 449. CUTANEOUS NERVES OF THE 

OUTER SIDE OF THE LEG AND FOOT 
(from Sappey after Hirschfeld and 
Leveille*). 

1, external popliteal nerve ; 2, its 
external cutaneous branch ; 3, communi- 
cating branch which unites with 4, that 
form the internal popliteal in 5, the ex- 
ternal saphenous nerve ; 6, calcaneal 
branch of the external saphenous; 7, 
external dorsal digital branch to the fifth 
toe ; 8, collateral dorsal digital branch 
of the fourth and fifth toes ; 9, musculo- 
cutaneous nerve ; 10, its cutaneous 
branches ; 11, loop of union with the 
external saphenous; 12, union between 
its outer and inner branches ; 13, an- 
terior tibial nerve, shown by the removal 
of a part of the muscles, and giving 
muscular branches superiorly ; 14, its 
terminal branch emerging in the space 
between the first and second toes, where 
it gives the collateral dorsal digital 
branches to their adjacent sides ; 15, 
branches to the peronei muscles. 

CUTANEOUS NERVES. The cuta- 
neous branches, two or three in 
number, supply the skin on the 
back part and outer side of the 
leg. 

The peroneal communicating 
branch (r. communicans fibularis), 
which joins the short sapheuous 
nerve below the middle of the 
back of the leg, is the largest of 
these nerves. In some instances, 
it continues a separate branch and 
its cutaneous filaments reach down 
to the heel or on to the outside of 
the foot. 

Another cutaneous branch extends along the outer side of the leg to the 
middle or lower part, sending offsets both backwards and forwards. 

MUSCULO-CUTANEOUS NERVE. 

The musculo-cutaneous (peroneal) nerve descends between the peronei 
muscles and the long extensor of the toes, and reaches the surface by per- 
forating the fascia in the lower part of the leg on the anterior aspect. It 
then divides into two branches, distinguished as external and internal, 
which proceed to the toes. The two branches sometimes perforate the 
fascia at a different height. 




PERONEAL NERVE. 



681 



(a) Muscular branches are given to the peroneus longus and peroneus brevis. 

(b) Cutaneous branches given off before the final division are distributed to the lower 
part of the leg. 

(c) The internal branch of the musculo-cutaneous nerve, passing forwards along 
the dorsum of the foot, furnishes one branch to the inner side of the great toe, and 
others to the contiguous sides of the second and third toes. It gives other offsets, 
which extend over the inner ankle and side of the foot. This nerve communicates 
with the long saphenous nerve on the inner side of the foot, and with the anterior 
tibial nerve between the first and second toes. 



Fig. 450. 



Fig. 450. VIEW OF THE DISTRIBUTION OP THE 
BRANCHES OP THE EXTERNAL POPLITEAL NERVE IN 
THE FRONT OP THE LEG AND DORSUM OF THE FOOT 
(from Hirschfeld and Leveille'). 

The upper part of the peroneus longus muscle has 
been removed, the tibialis anticus, the long extensor of 
the great toe and the peroneus longus have been drawn 
separate in the leg by hooks marked a, 6, and c, and 
the tendons of the extensor muscles have been removed 
in the dorsum of the foot, to show the deeper seated 
nerves ; 1, the external popliteal or peroneal nerve 
winding round the other part of the fibula ; 1', its 
recurrent articular branches exposed by the dissection 
of the upper part of the tibialis anticus muscle ; 2, 2, 
the musculo-cutaneous nerve ; 2', 2', twigs to the long 
and short peroneal muscles ; 3, internal branch of the 
musculo-cutaneous nerve ; 3', 3', its dorsal digital 
branches to the inside of the great toe, and to the 
adjacent sides of the second and third toes ; 4, the 
external branch ; 4', 4', its dorsal digital branches to 
the adjacent sides of the third and fourth toes, and in 
part to the space between the fourth and fifth toes ; 
5, the external saphenous nerve descending on the 
outer border of the foot, and uniting at two places 
with the outer branch of the musculo-cutaneous ; 5', 
its branch to the outer side of the fifth toe ; 6, placed 
on the upper part of the extensor communis digitorura, 
marks the anterior tibial nerve passing beneath the 
muscles ; 6, placed farther down on the tendon of the 
tibialis anticus, points to the nerve as it crosses to 
the inside of the anterior tibial artery ; 6', its muscular 
branches in the leg ; 6", on the tendon of the extensor 
longus pollicis points to the anterior tibial nerve after 
it has passed into the foot behind that tendon ; 7, 
its inner branch uniting with a twig of the musculo- 
cutaneous, and giving the dorsal digital nerves to the 
adjacent sides of the first and second toes; 8, distri- 
bution of its outer branch to the extensor brevis dlgi- 
torum and tarsal articulations. 



(d) The external branch, larger than the internal 
one, descends over the foot towards the fourth toe, 
which, together with the contiguous borders of the 
third and fifth toes, it supplies with branches. 

Cutaneous nerves, derived from this branch, spread over the outer ankle and the 
outer side of the foot, where they are connected with the short saphenous nerve. 

The dorsal digital nerves are continued on to the last phalanges of the toes. 

The number of toes supplied by each of the two divisions of the musculo-cuta- 
neous nerve is liable to vary ; together these nerves commonly supply all the toes on 
the dorsal aspect, excepting the outer side of the little toe, which receives a branch 
from the short saphenous nerve, and the adjacent sides of the gre.it toe and the second 
toe, to which the anterior tibial nerve is distributed : with this latter branch, how- 
ever, it generally communicates. 

Y Y 




682 SYNOPSIS OF CUTANEOUS NERVES. 

ANTERIOR TIBIAL NERVE. 

The anterior tibial (interosseous nerve), commencimg between the fibula 
and the ]:eroneus longus, inclines obliquely beneath the long extensor of 
the toes to the fore part of the interosseous membrane, and there comes 
into contact with the anterior tibial vessels, and with those vessels it 
descends to the front of the ankle-joint, where it divides into an external 
and an internal branch. The nerve first reaches the outer side of the 
anterior tibial artery, above the middle of the leg ; and, after crossing in 
front of that vessel once or oftener, lies to the inner side of it at the bend 
of the ankle. 

(a) Muscular branches. In its course along the leg, the anterior tibial nerve 
gives slender filaments to the muscles between which it is placed, namely, the tibialis 
anticus, the long extensor of the toes, and the special extensor of the great toe. 

(b) The external branch of the anterior tibial nerve turns outwards over the tarsus 
beneath the short extensor of the toes ; and, having become enlarged (like the pos- 
terior interosseous nerve on the wrist) terminates in branches which supply the short 
extensor muscle, and likewise the articulations of the foot. 

(c) The internal branch, continuing onwards in the direction of the anterior tibial 
nerve, accompanies the dorsal artery of the foot to the first interosseous space, and 
ends in two branches, which supply the integument on the neighbouring sides of the 
great toe and the second toe on their dorsal aspect. It communicates with the inter- 
nal division of the musculo-cutaneous nerve. 

Summary of the external popliteal nerve. This nerve supplies, besides 
articular branches to the knee, ankle, and foot, the peronei muscles, extensor 
muscles of the foot, also the integument of the front of the leg and dorsum 
of the foot. It gives the ramus communicans fibularis to the short 
saphenous branch of the internal popliteal nerve, and communicates with 
the long saphenous nerve. 

SYNOPSIS OF THE CUTANEOUS DISTRIBUTION OF THE 
CEREBRO-SPiNAL NERVES. 

HEAD. The face and head in front of the ear are supplied with sensory 
nerves from the fifth cranial nerve. The ophthalmic division supplies 
branches to the forehead, upper eyelid, and dorsum of the nose. The 
superior maxillary division supplies the cheek, ala of the nose, upper lip, 
lower eyelid, and the region behind the eye, over the temporal fascia. The 
inferior maxillary division supplies the chin and lower lip, the pinna of the 
ear on its outer side, and the integument in front of the ear and upwards to 
the vertex of the head. 

The head, behind the ear, is mainly supplied by the great occipital branch 
of the posterior division of the second spinal nerve, but above the occipital 
protuberance there is also distributed the branch from the posterior division of 
the third spinal nerve ; and, rn front of the area of the great occipital nerve, is 
a space supplied by anterior divisions of spinal nerves, viz., the back of the 
pinna of the ear, together with the integument behind and that in front over 
the parotid gland, which are supplied by the great auricular nerve ; while 
between the area of that nerve and the great occipital the small occipital 
nerve intervenes. The auricular branch of the pneumo-gastric nerve also 
is distributed on the back of the ear. 

TRUNK. The posterior divisions of the spinal nerves supply an area, 
extending on the back from the vertex of the skull to the buttock. This 
area is narrow in the neck ; it is spread out over the back of the scapula ; 



SYNOPSIS OF CUTANEOUS NERYES. 683 

and on the buttock the distribution of the lumbar nerves extends to the 
trochanters. 

The area supplied by the cervical plexus, besides extending upwards, as 
already mentioned, on the lateral part of the skull, stretches over the 
front and sides of the neck, and the upper part of the shoulder and breast. 

The area of the anterior divisions of the dorsal and Jirst lumbar nerves meets 
superiorly with that of the cervical plexus, and posteriorly with that of the 
posterior divisions of dorsal and lumbar nerves. It passes down over the 
haunch and along by the outer part of Pou part's ligament, and includes 
part of the scrotum and a small portion of the integument of the thigh 
internal to the saphenous opening. 

The perinceum and penis are supplied by the pudic nerve ; the scrotum by 
branches of the pudic, inferior pudendal, and ilio- inguinal nerves. 

UPPER LIMB. The shoulder, supplied superiorly by the cervical plexus, 
receives its cutaneous nerves iuferiorly as far as the insertion of the deltoid 
from the circumflex nerve. 

The arm internally is supplied by the intercosto-humeral nerve and the 
nerve of Wrisberg. The iuner and anterior part is supplied by the internal 
cutaneous nerve ; and the posterior and outer part by the internal and 
external branches of the musculo-spiral nerve. 

The forearm, anteriorly and on the outer side, is supplied by the 
external cutaneous ; on its outer and posterior aspect, superiorly by the 
external cutaneous branches of the musculo-spiral, and inferiorly by the 
radial branch of the same nerve. On the inner side, both in front and 
behind, is the internal cutaneous nerve, and inferiorly are branches of the 
ulnar. 

On the back of the hand are the radial and uluar nerves, the radial 
supplying about three fingers and a half or less, and the uluar one and a 
half or more. 

On the front of the hand, the median nerve supplies three fingers and a 
half, and the ulnar one and a half. In the palm is a branch of the median 
given off above the wrist. On the ball of the thumb are branches of the 
mu- culo-cutaneous, median, and radial nerves. 

LOWER LIMB. The buttock is supplied from above by the cutaneous 
branches of the posterior divisions of the lumbar nerves, with the ilio-hypo- 
gastric and lateral branches of the last dorsal nerves ; internally by the 
posterior divisions of the sacral nerves ; externally by the posterior branch 
of the external cutaneous nerve proceeding from the front ; and inferiorly 
by branches of the small sciatic nerve proceeding from below. 

The thigh is supplied externally by the external cutaneous nerve ; 
posteriorly, and in the upper half of its ii.ner aspect, by the small sciatic ; 
anteriorly, and in the lower half of the inner aspect, by the middle and 
internal cutaneous. 

The leg is supplied posteriorly by the small sciatic and short saphenous 
nerves ; internally by the long saphenous and branches of the internal 
cutaneous of the thigh ; and outside and in front by cutaneous branches of 
the external popliteal nerve, and by its musculo- cutaneous branch. 

On the dorsum of the foot are the branches of the mu^culo-cutaneous, 
supplying all the toes with the exception of the adjacent sides of the first 
and second, which are supplied by the anterior tibial, and the outer side of 
the little toe, which, with the outer side of the foot, is supplied by the short 
saphenous nerve. The long saphenous is the cutaneous nerve on the inner 
side of the foot. 

Y Y 2 



684 SYNOPSIS OF MUSCULAR NERVES. 

The sole of the foot is supplied by the plantar nerves. The internal 
plantar nerve gives branches to three toes and a half ; the external to the 
remaining one toe and a half. 

SYNOPSIS OF THE MUSCULAR DISTRIBUTION OF THE 
CEREBRO-SPINAL NERVES. 

MUSCLES OF THE HEAD AND FORE PART OF THE NECK. 

The muscles of the orbit are mostly supplied by the third cranial nerve 
the superior division of that nerve being distributed to the levator palpebrzo 
and the superior rectus muscles ; and the inferior division to the inferior and 
internal recti and the inferior oblique. The superior oblique muscle is supplied 
by the fourth nerve, the external rectus by the sixth ; while the tensor 
tarsi has no special nerve apart from those of the orbicularis palpebrarum, 
which are derived from the facial. 

The superficial muscles of the face and scalp, which are associated in their 
action as a group of muscles of expression, are supplied by the portio dura 
of the seventh cranial nerve ; the retrahens auriculam arid occipitalis 
muscles being supplied by the posterior auricular branch. 

The deep muscles of the face, employed in mastication, viz., the temporal, 
masseler, buccinator, and two pterygoid muscles, are supplied by the inferior 
maxillary division of the fifth cranial nerve. 

Muscles above the hyoid bone. The mylo-hyoid muscle and anterior belly 
of the digastric are supplied by a special biauch of the inferior maxillary 
division of the fifth cranial nerve ; the posterior belly of the digastric 
muscle, and the stylo-hyoid, are supplied by branches of the portio dura. The 
genio-hyoid and the muscles of the tongue receive their nervous supply 
from the hypoglossal nerve. 

The muscles ascending to the hyoid bone and laiynx, viz., the sterno-hyoid, 
omo-hyoid, and sterno-thyroid, are supplied from the ramns descendens noni 
and its loop with the cervical plexus, while the thyro-hyoid muscle receives 
a separate twig from the ninth nerve. 

The larynx, pharynx, and soft palate. The crico- thyroid muscle is sup- 
plied by the external laryngeal branch of the pneumo-gastric nerve, and the 
other intrinsic muscles of the larynx by the recurrent laryngeal. The 
muscles of the pharynx are supplied principally by the pharyngeal branch of 
the pneumo -gastric ; the stylo-pharyngeus, however, is supplied by the 
glosso-pharyngeal nerve. Of the muscles of the soft palate unconnected 
with the tongue or pharynx, the tensor palati receives its nerve from the otic 
ganglion (which also supplies the tensor tympani); the levator palati gets a 
twig (Meckel) from the posterior palatine branch of the spheno-palatiue 
ganglion, and the azygos uvulee is probably supplied from the same source. 

MUSCLES BELONGING EXCLUSIVELY TO THE TRUNK, AND MUSCLES 
ASCENDING TO THE SKULL. 

All those muscles of the back which are unconnected with the upper limb, 
viz., the posterior serrati, the splenius, complexus, erector spiuse, and the 
muscles more deeply placed, receive their supply from the posterior divisions 
of the spinal nerves. 

The sterno-mastoid is supplied by the spinal accessory nerve and a twig 
of the cervical plexus coming from the second cervical nerve. 



SYNOPSIS OF MUSCULAR NERVES. 6?5 

The rectus capitis anticus major ar,d minor are supplied by twigs from the 
upper cervical nerves ; the longus colli and scaleni muscles by twigs from 
the lower cervical nerves. 

The muscles of the chest, viz , the intercostals, subcostals, levatores cos- 
tarum, arid triangularis sterni, are supplied by the intercostal nerves. 

The obliqui, transversus, and rectus of the abdomen are supplied by the 
lower intercostal nerves ; and the oblique and transverse muscles also get 
branches from the ilio-inguiual and ilio hypogastric nerves. The cremaster 
muscle is supplied by the genital branch of the genito-crural nerve. 

The quadratus lumborum (like the psoas) receives small branches from 
the lumbar nerves before they form the plexus. 

The diaphragm receives the phrenic nerves from the fourth and fifth cer- 
vical nerves, and likewise sympathetic filaments from the plexuses round the 
phrenic arteries. 

The muscles of the urethra and penis are supplied by the pudic nerve ; 
the levator and sphincter ani by the pudic an.l by the fourth and fifth 
S'icrai and the coccygeal nerves ; and the coccyyeus muscle by the three last 
named nerves. 

MUSCLES ATTACHING THE UPPER LIMB TO THE TRUNK. 

The trapezius and the sterno-cleido-mastoid receive the distribution of the 
spinal accessory nerve, and, in union with it, filaments from the cervical 
plexus. 

The latissimus dorsi receives the long subscapular nerve. 

The rhomboidei are supplied by a special branch from the anterior 
division of the fifth cervical nerve. 

The levator anguli scapulae is supplied by branches from the anterior 
division of the third cervical nerve, and sometimes partly also by the branch 
to the rhomboid muscles. 

The serratus majnus has a special nerve, the posterior thoracic, derived 
from the fifth and sixth cervical nerves. 

The subclavius receives a special branch from the place of union of the 
fifth and sixth cervical nerves. 

The pectorales are supplied by the anterior thoracic branches of the 
brachial plexus, the larger muscle receiviug filaments from both these 
nerves, and the smaller from the inner only. 

MUSCLES OF THE UPPER LIMB. 

Muscles of the shoulder. The supraspinatus and infraspinatus are sup- 
plied by the suprascapular nerve ; the subsoapularis by the two smaller 
subscapular nerves ; the teres major by the second subscapular, and the 
deltoid and teres minor by the circumflex nerve. 

Posterior muscles of the arm and forearm. The triceps, anconeus, supi- 
nator longus, and extensor carpi radialis Lmgior are supplied by direct branches 
of the musculo-spiral nerve ; while the extensor carpi radialis brevior and the 
other extensor muscles iti the forearm receive their branches from the pos- 
terior iuterosseous division of that nerve. 

Anterior muscles of the arm and forearm. The coraco-brachialis, biceps, 
and brachialis anticus are supplied by the musculo- cutaneous nerve : the 
brachialis anticus likewise generally receives a twig from the musculo- 
spiral nerve. The muscles in front of the forearm are supplied by the 
median nerve, with the exception of the flexor carpi uluaris and the 
ulnar half of the flexor profuudus digitorum, which are supplied by the 



G86 THE SYMPATHETIC NERVES. 

ulnar nerve, and the supinator longus, which is supplied by the musculo- 
spiral. 

Muscles of the hand. The abductor and opponens pollicis, the outer half 
of the flexor brevis pollicis, and the two outer lumbricales muscles, are 
supplied by the median nerve : all the other muscles receive their nerves 
from the ulnar. 

MUSCLES OF THE LOWER LIMB. 

Posterior muscles of the hip and thigh. The gluteus maximus is mainly 
supplied by the small sciatic nerve, and receives at its upper part a separate 
branch from the sacral plexus. The gluteus medius and minimus, together 
with the tensor vaginse femoris, are supplied by the gluteal nerve. The pyri- 
formis, gemelli, obturator iiiternus, and quadratus femoris receive special 
branches from the sacral plexus. The hamstring muscles are supplied by 
branches from the great sciatic nerve. 

Anterior and internal muscles of the thigh. The psoas muscle is supplied 
by separate twigs from the lumbar nerves. The iliacus, quadriceps extensor 
femoris, and sartorius are supplied by the anterior crural nerve. The 
adductor muscles, the obturator externus and the pectineus, are supplied 
by the obturator nerve, but the adductor maguus likewise receives a branch 
from the great sciatic, and the pectineus sometimes has a branch from the 
anterior crural. 

Anterior muscles of the leg and foot. The muscles in front of the leg, 
together with the extensor brevis digitorum, are supplied by the anterior 
tibia! nerve. 

The peroneus longus and brevis are supplied by the musculo-cutaneous 
nerve. 

Posterior muscles of the leg. The gastrocnemius, plantaris, soleus, and 
popliteus are supplied by branches from the internal popliteal nerve ; the 
deep muscles, viz., the flexor longus digitorum, flexor longus pollicis, and 
tibialis posticus, derive their nerves from the posterior tibial. 

Plantar muscles. The flexor brevis digitorum, the abductor and flexor 
brevis pollicis, and the two inner lumbricales, are supplied by the internal 
plantar nerve ; all the others, including the flexor accessorius and iuterossei, 
are supplied by the external plantar nerve. 



III. SYMPATHETIC NERVES. 

The nerves of the sympathetic system (nervus intercostalis ; nerves of 
organic life Bichat) are distributed in general to all the internal viscera, 
but some organs receive their nerves also from the cerebro spinal system, 
as the lungs, the heart, and the upper and lower parts of the alimentary 
canal. It appears from physiological researches to be also the special 
province of the sympathetic system to supply nerves to the coats of the 
blood-vessels. 

This division of the nervous system consists of a somewhat complicated 
collection of ganglia, cords and plexuses, the parts of which may, for con- 
venience, be classified in three groups, viz., the principal gangliated cords, 
the great prevertebral plexuses with the nerves proceeding from them, and 
the ganglia of union with cranial nerves. 

The gangliated cords consist of two series, in each of which the ganglia are 
connected by intervening cords. These cords are placed symmetrically in. 



GAXGLIATED SYMPATHETIC COEDS. 



687 



front of the vertebral column, and extend 
from the base of the skull to the coccyx. 
Superiorly they are connected with plex- 
uses which enter the cranial cavity, while 
iuferiorly they converge on the sacrum, 
and terminate in a single ganglion on the 
coccyx. The several portions of the cords 
are distinguished as cervical, dorsal, lum- 
bar, and sacral, and iu each of these parts 
the ganglia are equal in number, or nearly 
so, to the vertebrae on which they lie, 
except in the neck, where there are only 
three. 

Fig. 451. DIAGRAMMATIC OUTLINE OF THE SYM- 
PATHETIC CORD OF ONE SIDE IN CONNECTION 

WITH THE SPINAL NERVES. 

The full description of this figure will be found 
at p. 629. 

On the right side the following letters in- 
dicate parts of the sympathetic nerves ; viz. 
a, the superior cervical ganglion, communi- 
cating with the upper cervical spinal nerves 
and continued below into the great sympathetic 
cord ; 6, the middle cervical ganglion ; c, d, the 
lower cervical ganglion united with the first 
dorsal ; d', the eleventh dorsal ganglion ; from 
the fifth to the ninth dorsal ganglia the origins 
of the great splanchnic nerve are shown ; I, the 
lowest dorsal or upper lumbar ganglion ; ss, the 
upper sacral ganglion. In the whole extent of the 
sympathetic cord, the twigs of union with the 
spinal nerves are shown. 

Connection of the ganyliated cords with 
the c&rebro-spinal system. The ganglia are 
severally connected with the spinal nerves 
in their neighbourhood by means of short 
cords ; each connecting cord consisting of 
a white and a grey portion, the former 
of which may be considered as proceeding 
from the spinal nerve to the ganglion, 
the latter from the ganglion to the spinal 
nerve. At its upper end the gangliated 
cord communicates likewise with certain 
cranial nerves. The main cords interven- 
ing between the ganglia, like the smaller 
ones connecting the ganglia with the spinal 
nerves, are composed of a grey and a white 
part, the white being continuous with the 
fibres of the spinal nerves prolonged to the 
ganglia. 

The great prevertebral plexuses comprise 
three large aggregations of nerves, or 
nerves and ganglia situated in front of 
the spine, and occupying respectively the 
thorax, the abdomen, and the pelvis, 
They are single and median, and are 



Fig. 451. 



Br 



688 THE SYMPATHETIC NERVES. 

named respectively the cardiac, the solar, and the hypogastric plexus. 
These plexuses receive branches from both the gangliated cords above 
noticed, and they constitute centres from which the viscera are supplied 
with nerves. 

The cranial ganglia of the sympathetic are the ophthalmic, spheno-pala- 
tine, subrn axillary, and otic, which, being intimately united with the fifth 
cranial nerve, have already been described along with that nerve. They 
nre also more or less directly connected with the upper end of the sympa- 
thetic gangliated cords ; but it will be unnecessary to give any special 
description of them in this place. 

A. THE GANGLIATED COEDS. 
THE CERVICAL PART. 

In the neck, each gangliated cord is deeply placed behind the sheath of 
the great cervical blood-vessels, and in contact with the muscles which 
immediately cover the fore part of the vertebral column. It comprises 
three ganglia, the first of which is placed near the base of the skull, the 
second in the lower part of the neck, and the third immediately above the 
head of the first rib. 

THE UPPER CERVICAL GANGLION. 

This is the largest ganglion of the great sympathetic cord. It is continued 
p.uperiorly into an ascending branch, and tapers below into the connecting 
cord, so as to present usually a fusiform shape ; but there is considerable 
variety in this respect in different cases, the ganglion being occasionally 
broader than usual, and sometimes constricted at intervals. It has the 
reddish-grey colour characteristic of the ganglia of the sympathetic system. 
It is placed on the larger rectus muscle, opposite the second and third 
cervical vertebrae, and behind the internal carotid artery. 

Connection with spinal nerves. At its outer side the superior cervical 
ganglion is connected with the first four spinal nerves, by means of slender 
cords, which have the structure pointed out in the general description as 
being common to the series. 

The circumstance of this ganglion being connected with so many as four spinal 
nerves, together with its occasionally constricted appearance, is favourable to the 
view that it may be regarded as consisting of several ganglia which have coalesced. 

Connection irith cranial nerves. Small twigs connect the ganglion or 
its cranial cord with the second ganglion of the pneumo-gastric, and with 
the ninth cranial nerve, near the base of the skull ; and another branch, 
which is directed upwards from the ganglion, divides at the base of the 
skull into two filaments, one of which ends in the second (petrosal) ganglion 
of the glosso-pharyngeal nerve ; while the other, entering the jugular 
foramen, joins the ganglion of the root of the pneumo-gastric. 

Besides the branches connecting it with cranial and spinal nerves, the 
first cervical ganglion gives off also the ascending branch, the upper cardiac 
nerve, pharyngeal nerves, and branches to blood-vessels. 

1. ASCENDING BRANCH AND CRANIAL PLEXUSES. 

The ascending branch of the first cervical ganglion is soft in texture and of 



CAROTID BRANCH AND PLEXUS. 689 

a reddish tint, seeming to be in some degree a prolongation of the ganglion 
itself. In its course to the skull, it is concealed by the internal carotid 
artery, with which it enters the carotid canal in the temporal bone, and it is 
then divided into two parts, which are placed one on the outer, the other on 
the inner side of the vessel. 

Fig. 452 




Fig. 452. CONNECTIONS OP THE SYMPATHETIC NERVE THROUGH ITS CAROTID BRANCH 

WITH SOME OP THE CRANIAL NERVES. 

The full description of this figure will be found at p. 602. The following numbers 
refer to sympathetic nerves and their connections : 6, spheno-palatine ganglion ; 7, 
Vidian nerve ; 9, its carotid branch ; 10, a part of the sixth nerve, receiving twigs from 
the carotid plexus of the sympathetic; 11, superior cervical sympathetic ganglion; 12, 
its prolongation in the carotid branch ; 15, anastomosing nerve of Jacobson ; 16, twig 
uniting it to the sympathetic. 

The external division distributes filaments to the internal carotid artery, 
and, after communicating by means of other filaments with the internal 
division of the cord, forms the carotid plexus. 

The inner division, rather the smaller of the two, supplies filaments to 
the carotid artery, and goes to form the cavernous plexus. The terminal 
parts of these divisions of the cranial cord are prolonged on the trunk of the 
internal carotid, and extend to the cerebral and ophthalmic arteries, around 
which they form secondary plexuses, those on the cerebral artery ascending 
to the pia mater. One minute plexus enters the eye-ball with the central 
artery of the retina. 

It was stated by Ribes (Mem. de la Socie"te Med. d'Emulation, torn. viii. p. 606,) that 
the cranial prolongations of the sympathetic nerve from the two sides coalesce with 
one another on the anterior communicating artery, a small ganglion or a plexus 
being formed at the point of junction; but this connection has not been satis- 
factorily made out by other observers. 

CAROTID PLEXUS. The carotid plexus, situated on the outer side of the 
internal carotid artery at its second bend (reckoning from below), or between 
the second and third bends, joins the fifth and sixth cranial nerves, and 
gives many filaments to the vessel on which it lies. 

Branches. (a) The connection with the sixth nerve is established by means of one 
or two filaments of considerable size, which are supplied to that nerve where it lies 
by the side of the internal carotid artery. 



690 THE SYMPATHETIC NERVES. 

(6) The filaments connected with the Gasserian ganglion of the fifth nerve pro- 
ceed sometimes from the carotid plexus, at others from the cavernous. 

(c) The deep branch of the Vidian nerve passes backwards to the carotid plexus, 
and after leaving the Vidian canal, lies in the cartilaginous substance which closes 
the foramen lacerum medium. Valentin describes nerves as furnished to the dura 
mater from the carotid plexus. 

CAVERNOUS PLEXUS. The cavernous plexus, named from its position in 
the sinus of the same name, is placed below and rather to the inner side of 
the highest turn of the internal carotid artery. Besides giving branches on 
the artery, it communicates with the third, the fourth and the ophthalmic 
of the fifth cranial nerves. 

Blanches. (a) The filament which joins the third nerve comes into connection 
with it close to the point of division of that nerve. 

(b) The branch to the fourth nerve, which may be derived from either the caver- 
nous or the carotid plexus, joins the nerve where it lies in the wall of the cavernous 
sinus. 

(c) The filaments connected with the ophthalmic trunk of the///* nerve are supplied 
to its inner surface. One of them is continued forwards to the lenticular ganglion, 
either in connection with or distinct from the nasal nerve. 

2. PHARYNGEAL NERVES AND PLEXUS. 

These nerves arise from the inner part of the ganglion, and are directed 
obliquely inwards to the side of the pharynx. Opposite the middle con- 
strictor muscle they unite with branches of the pneumo-gastric and glosso- 
pharyngeal nerves ; and by their union with those nerves the pliaryngeal 
plexus is formed. Branches emanating from the plexus are distributed 
to the muscles and mucous membrane of the pharynx. 

3. UPPER CARDIAC NERVE. 

Each of the cervical ganglia of the sympathetic furnishes a cardiac branch, 
the three being named respectively the upper, middle and lower cardiac 
nerves. 

These branches are continued singly, or in connection, to the large 
prevertebral centre (cardiac plexus) of the thorax. Their size varies con- 
siderably, and where one branch is smaller than common, another will be 
found to be increased in size, as if to compensate for the defect. There 
are some differences in the disposition of the nerves of the right and left 
sides. 

The upper cardiac nerve (n. cardiacus superficialis) of the right side 
proceeds from two or more branches of the ganglion, with, in some 
instances, an offset from the cord connecting the first two ganglia. In its 
course down the neck the nerve lies behind the carotid sheath, in contact with 
the longus colli muscle ; and it is placed in front of the lower thyroid artery 
and the recurrent laryngeal nerve. Entering the thorax, it passes in some 
cases before, in others behind the subclavian artery, and is directed along the 
innominate artery to the back part of the arch of the aorta, where it ends in 
the deep cardiac plexus, a few small filaments continuing also to the front 
of the great vessel. Some branches distributed to the thyroid body 
accompany the inferior thyroid artery. 

In its course downwards the cardiac nerve is repeatedly connected with] other 
branches of the sympathetic, and with the pneumo-gastric nerve. Thus about the 
middle of the neck it is joined by some filaments from the external laryngeal 



UPPER CARDIAC XERVE. 



691 



nerve; and, rather lower down, by one or more filaments from the trunk of the 
pneumo-gastric nerve ; lastly, on entering the chest, it joins with the recurrent 
laryngeal. 

Fig. 453. 




Fig. 453. CONNECTIONS OF THE CERVICAL AND UPPER DORSAL SYMPATHETIC GANGLIA 
AND NERVES ON THE LEFT SIDE. 

The full description of this figure will be found at p. 620. The following numbers 
refer to the sympathetic ganglia and nerves, and those immediately connected with 
them : 3, pharyngeal plexus ; 8, laryngeal plexus ; 13, pulmonary plexus ; and to 
the reader's left, above the pulmonary artery, a part of the cardiac plexus ; 24, superior 
cervical ganglion of the sympathetic ; 25, middle cervical ganglion ; 26, inferior cervical 
ganglion united with the first dorsal ganglion ; 27, 28, 29, 30, second, third, fourth, and 
fifth dorsal ganglia. 

Variety. Instead of passing to the thorax in the manner described, the superior 
cardiac nerve may join the cardiac branch furnished from one of the other cer- 
vical ganglia. Scarpa describes this as the common disposition of the nerve ; 
but Cruveilhier (Anat. Descript., t. iv.) states that he has not in any case 
found the cardiac nerves to correspond exactly ^ith the figures of the " Tabula* 
Xeurologicae." 



692 THE SYMPATHETIC NERVES. 

The superficial cardiac nerve of the left side has, while in the neck, the 
same course and connections as that of the right side. But within the 
chest it follows the left carotid artery to the arch of the aorta, and ends in 
some instances in the superficial cardiac plexus, while in others it joins the 
deep plexus ; and accordingly it passes either in front of or behind the arch 
of the aorta. 

4. BRANCHES TO BLOOD-VESSELS. 

The nerves which ramify on the arteries (nervi molles) spring from the 
front of the ganglion, and twine round the trunk of the carotid artery. 
They are prolonged on each branch of the external carotid, and form 
slender plexuses upon them. 

Communications with other nerves. From the plexus on the facial artery is derived 
the filament which joins the submaxillary ganglion ; and, from that on the middle 
meningeal artery, twigs have been described as extending to the otic ganglion, as 
well as to the gangliform enlargement of the facial nerve. Lastly, a communication 
is established between the plexus on the carotid artery, and the digastric branch of 
the facial nerve. 

Small ganglia are occasionally found on some of the vascular plexuses, 
close to the origin of the vessels with which they are associated. Thus 
lingual, temporal, and pharyngeal ganglia have been described ; and besides 
these there is a larger body, the ganglion intercaroticum, placed on the 
inner side of the angle of division of the common carotid artery. This body, 
long known to anatomists as a ganglion, has been stated by Luschka to 
have a structure very different from the nervous ganglia in general, and has 
been named by him the "glandula intercarotica. " 

The ganglion intercaroticum was described by Luschka as presenting principally 
a follicular structure, and regarded by him as being of a nature similar to the glan- 
dula coccygea, which he had previously discovered. It appears, however, from the 
researches of Julius Arnold, that the follicular appearances observed by Luschka, both 
in this instance and in the coccygeal gland, were produced by arterial glomeruli seen 
in section; and that the ganglion intercaroticum consists of numbers of those glome- 
ruli gathered into several larger masses, and of dense plexuses of nerves surrounding 
respectively the glomeruli, the masses, and the whole structure. Within those plex- 
uses nerve-cells are scattered, but not in very great number. The ganglion is usually 
about one-fourth of an inch long ; but, according to Luschka, may be divided into 
small separate masses, and thus escape attention, or be supposed to be absent. 
(Luschka, Anat. d. Menschen, vol. i. 1862 ; and Julius Arnold, in Virchow's Archiv., 
June, 1865.) 

MIDDLE CERVICAL GANGLION. 

The middle ganglion (ganglion thyroideum), much the smallest of the 
cervical ganglia, is placed on or near the inferior thyroid artery. It is 
usually connected with the fifth and sixth spinal nerves, but in a somewhat 
variable manner. It gives off thyroid branches and the middle cardiac 
nerve. 

THYROID BRANCHES. From the inner side of the ganglion some twigs 
proceed along the inferior thyroid artery to the thyroid body, where they 
join the recurrent laryngeal and the external laryngeal nerves. Whilst on 
the artery, these branches communicate with the upper cardiac nerve. 

THE MIDDLE CARDIAC NERVE (nervus cardiacus profundus v. magnus) of the 
right side is prolonged to the chest behind the sheath of the common carotid 
artery, and either in front of or behind the subclavian artery. In the 



LOWER CEHVICAL GANGLION. 693 

chest it lies on the trachea, where it is joined by filaments of the recurrent 
laryngeal nerve, and it ends in the right side of the deep cardiac plexus. 
While in the neck, the nerve communicates with the upper cardiac nerve 
and the recurrent branch of the pueumo-gastric. 

On the left side, the middle cardiac nerve enters the chest between the 
left carotid and subclavian arteries, and joins the left side of the deep 
cardiac plexus. 

AVhen the middle cervical ganglion is small, the middle cardiac nerve may be 
found to be an offset of the inter-ganglionic cord. 

LOWER CERVICAL GANGLION". 

The lower or third cervical ganglion is irregular in shape, usually some- 
what flattened and round or semiluuar, and is frequently united in part 
to the first thoracic ganglion. Placed in a hollow between the transverse 
process of the last cervical vertebra and the neck of the first rib, it is con- 
cealed by the vertebral artery. It is connected by short communicating 
cords with the two lowest cervical nerves. Numerous branches are given 
oif from it, among which the largest is the lower cardiac nerve. 

THE LOWER CARDIAC NERVE, issuing from the third cervical ganglion or 
from the first thoracic, inclines inwards on the right side, behind the sub- 
clavian artery, and terminates in the cardiac plexus behind the arch of the 
aorta. It communicates with the middle cardiac and recurrent laryngeal 
nerves behind the subclavian artery. 

On the left side, the lower cardiac often becomes blended with the middle 
cardiac nerve, and the cord resulting from their union terminates in the 
deep cardiac plexus. 

BRANCHES TO BLOOD-VESSELS. From the lowest cervical and first dorsal 
ganglia a few slender branches ascend along the vertebral artery in its 
osseous canal, forming a plexus round the vessel by their inter-communica- 
tions, and supplying it with offsets. This plexus is connected with the 
cervical spinal nerves as far upwards as the fourth. 

One or two branches frequently pass from the lower cervical ganglion to 
the first dorsal ganglion in front of the subclavian artery, forming loops 
round the vessel (ansse Vieussenii), and supplying it with small offsets. 

THORACIC PART OF THE GANGLIATED CORD. 

In the thorax the gangliated cord is placed towards the side of the spinal 
column, in a line passing over the heads of the ribs. It is covered by the 
pleura, and crosses the intercostal blood-vessels. 

Opposite the head of each rib the cord usually presents a ganglion, 
so that there are commonly twelve of these ; but, from, the occasional 
coalescence of two, the number varies slightly. The first ganglion when 
distinct is larger than the rest, and is of an elongated form ; but it is often 
blended with the lower cervical ganglion. The rest are small, generally 
oval, but very various in form. 

Connection with the spinal nerves. The branches of connection between 
the spinal nerves and the ganglia of the sympathetic are usually two in 
number for each ganglion ; one of these generally resembling the spinal 
nerve in structure, the other more similar to the sympathetic nerve. 

BRANCHES OF THE GANGLIA. 

The branches furnished by the first fivt or six ganglia are small, and are 



946 



THE SYMPATHETIC NERVES. 



Fig. 451 




THORACIC GAXGLIA. 695 

Fig. 451. DIAGRAMMATIC VIEW OP THE SYMPATHETIC CORD OP THE RIGHT SIDT-, SHOWING 

ITS CONNECTIONS WITH THE PRINCIPAL CEREBRO-SPINAL NERVES AND THE MAIN 

PREAORTIC PLEXUSES. 

Cerebro-spinal Nerves. VI, a portion of the sixth cranial nerve as it passes through 
the cavernous sinus, receiving two twigs from the carotid plexus of the sympathetic nerve; 
0, ophthalmic ganglion connected by a twig with the carotid plexus ; M, connection of the 
spheno-palatine ganglion by the Vidian nerve with the carotid plexns ; C, cervical plexus; 
Br, brachial plexus ; D 6, sixth intercostal nerve ; D 12, twelfth ; L 3, third lumbar 
nerve; S 1, first sacral nerve ; S 3, third ; S 5, fifth ; Cr, anterior crural nerve ; Cr', great 
sciatic ; pn, pneumo-gastric nerve in the lower part of the neck ; r, recurrent nerve 
winding round the subclaviau artery. 

Sympathetic Cord. c, superior cervical ganglion ; </, second or middle; c", inferior; 
from each of these ganglia cardiac nerves (all deep on this side) are seen descending to 
the cardiac plexus; d 1, placed immediately below the first dorsal sympathetic ganglion : 
d 6, is opposite the sixth; 11, first lumbar ganglion; eg, the terminal or coccygeal 
ganglion. 

Preaortic and Visceral Plexuses. pp, pharyngeal, and, lower down, laryngeal 
plexus ; p I, posterior pulmonary plexus spreading from the pneumo-gastric on the back 
of the right bronchus ; c a, on the aorta, the cardiac plexus, towards which, in addition 
to the cardiac nerves from the three cervical sympathetic ganglia, other branches are seen 
descending from the pneumo-gastric and recurrent nerves ; c o, right or posterior, and c o', 
left or anterior coronary plexus ; o, cesophageal plexus in long meshes on the gullet ; sp, 
great splanchnic nerve formed by branches from the fifth, sixth, seventh, eighth, and 
ninth dorsal ganglia; +, small splanchnic from the ninth and tenth ; + +, smallest or 
third splanchnic from the eleventh : the first and second of these are shown joining the 
solar plexus, so; the third descending to the renal plexus, re; connecting branches 
between the solar plexus and the pneumo-gastric nerves are also represented ; p n', above 
the place where the right pneumo-gastric passes to the lower or posterior surface of the 
stomach ; p n", the left distributed on the anterior or upper surface of the cardiac portion 
of the organ : from the solar plexus large branches are seen surrounding the arteries of 
the cceliac axis, and descending to m s, the superior mesenteric plexus ; opposite to this 
is an indication of the suprarenal plexus ; below r e (the renal plexus), the spermatic 
plexus is also indicated ; a o, on the front of the aorta, marks the aortic plexus, formed 
by nerves descending from the solar and superior mesenteric plexuses and from the lumbar 
ganglia ; m i, the inferior mesenteric plexus surrounding the corresponding artery ; h y, 
hypogastric plexus placed between the common iliac vessels, connected above with the 
aortic plexus, receiving nerves from the lower lumbar ganglia, and dividing below into the 
right and left pelvic or inferior hypogastric plexuses ; p I, the right pelvic plexus ; from 
this the nerves descending are joined by those from the plexus on the superiorjiemor- 
rhoidal vessels, m i', by sympathetic nerves from the sacral ganglia, and by numerous 
visceral nerves from the third and fourth sacral spinal nerves, and there are thus formed 
the rectal, vesical, and other plexuses, which ramify upon the viscera from behind for- 
wards and from below upwards, as towards i r, and v, the rectum and bladder. 

distributed in a great measure to the thoracic aorta, the vertebrae, and liga- 
ments. Several of these branches enter the posterior pulmonary plexus. 

The branches furnished by the lower six or seven ganglia unite into three 
cords on each side, which pass down to join plexuses in the abdomen, and 
are distinguished as the great, the small, and the smallest splanchnic nerve. 

THE GREAT SPLANCHNIC NERVE. 

This nerve is formed by the union of small cords (roots) given off by the 
thoracic ganglia from the fifth or sixth to the ninth or tenth inclusive. By 
careful examination of specimens after immersion in acetic or diluted nitric 
acid, small filaments may be traced from the splanchnic roots upwards as 
far aa the third ganglion, or even as far as the first (Beck, in the " Philo- 
sophical Transactions," Part 2, for 1846). 

Gradually augmented by the successive addition of the several roots, the 
cord descends obliquely inwards over the bodies of the dorsal vertebrae ; 
and, after perforating the crus of the diaphragm at a variable point, termi- 



696 THE SYMPATHETIC NEEYES. 

Dates in the semilunar ganglion, frequently sending some filaments to the 
renal plexus and the suprarenal body. 

The splanchnic nerve is remarkable from its white colour and firmness, 
which are owing to the preponderance of the spinal nerve-fibres in its 
composition. 

In the chest the great splanchnic nerve is not unfrequently divided into parts, and 
forms a plexus with the small splanchnic nerve. Occasionally also a small ganglion 
(ganglion splanchnicum) is formed on it over the last dorsal vertebra, or the last but 
one ; and when it presents a plexiform arrangement, several small ganglia have been 
observed on its divisions. 

In eight instances out of a large number of bodies, Wrisberg observed a fourth 
splanchic nerve (nervus splanclmicus supremus). It is described as formed by 
offsets from the cardiac nerves, and from the lower cervical as well as some of 
the upper thoracic ganglia. (" Observ. Anatom. de Nerv. Viscerum particula 
prima," p. 25, sect. 3.) 

SMALL SPLANCHNIC NERVE. 

The small or second splanchnic nerve springs from the tenth or eleventh 
ganglia, or from the neighbouring part of the cord. It passes along with the 
preceding nerve, or separately through the diaphragm, and ends in the 
coeliac plexus. In the chest this nerve often communicates with the large 
splanchnic nerve ; and in some instances it furnishes filaments to the renal 
plexus, especially if the lowest splanchnic nerve is very small or wanting. 

SMALLEST SPLANCHNIC NERVE. 

This nerve (nerv. renalis posterior Walter) arises from one of the lowest 
thoracic ganglia, and communicates sometimes with the nerve last described. 
After piercing the diaphragm, it ends in the renal plexus, and in the inferior 
part of the coeliac plexus. 

LUMBAR PART OF THE GANGLIATED CORD. 

In the lumbar region the two gangliated cords approach one another 
more nearly than in the thorax. They are placed before the bodies of the 
vertebrae, each lying along the inner margin of the psoas muscle ; and that 
of the right side is partly covered by the vena cava. 

The ganglia are small, and of an oval shape. They are commonly four 
in number, but occasionally, when their number is diminished, they are of 
larger size. 

Connection with spinal nerves. In consequence of the greater distance at 
which the lumbar ganglia are placed from the intervertebral foramina, the 
branches of connection with the spinal nerves are longer than in other 
parts of the gangliafced cord. There are generally two connecting branches 
for each ganglion, but the number is not so uniform as it is in the chest ; 
nor are those belonging to any one ganglion connected always with the 
same spinal nerve. The connecting branches accompany the lumbar arte- 
ries, and, as they cross the bodies of the vertebrae, are covered by the 
fibrous bauds which give origin to the larger psoas muscle. 

BRANCHES. The branches of these ganglia are uncertain in their number. 
Some join a plexus on the aorta ; others descending go to form the hypo- 
gastric plexus. Several filaments are distributed to the vertebrae and the 
ligaments connecting them. 

SACRAL PART OF THE GANGLIATED CORD. 
Over the sacrum the gangliated cord of the sympathetic nerve is much 



SACRAL GANGLIA. 69? 

diminished in size, and gives but few branches to the viscera. Its position 
on the front of the sacrum is along the inner side of the anterior sacral 
foramina ; and, like the two series of those foramina, the two cords approach 
one another in their progress downwards. The upper end of each is con- 
nected with the last lumbar ganglion by a single or a double iuterganglionic 
cord ; and at the lower end, they are connected by means of a loop with 
a single median ganglion, ganglion impar, placed on the fore part of the 
coccyx. The sacral ganglia are usually five in number ; but the variation 
both in size and number is more marked in these than in the thoracic 
or lumbar ganglia. 

Connection with spinal nerves. From the proximity of the sacral ganglia 
to the spinal nerves at their emergence from the foramina, the com- 
municating branches are very short : there are usually two for each ganglion, 
and these are in some cases connected with different sacral nerves. The 
coccygeal nerve communicates with the last sacral, or the coccygeal ganglion. 

Branches. The branches proceeding from the sacral ganglia are much 
smaller than those from other ganglia of the cord. They are for the 
most part expended on the front of the sacrum, and join the corresponding 
branches from the opposite side. Some filaments from one or two of the 
first ganglia enter the hypogastric plexus, while others go to form a plexus 
on the middle sacral artery. From the loop connecting the two cords on 
which the coccygeal ganglion is formed, filaments are given to the coccyx 
and the ligaments about it, and to the coccygeal glaud. 



COCCYGEAL GLA.ND. 

Under this name has been described by Luschka a minute structure, 
which has since received the attention of a number of writers. It is 
usually, according to Luschka, of the size of a lentil, and sometimes as large 
as a small pea ; its colour is reddish grey ; its surface lobulated ; and it 
occupies a hollow at the tip of the coccyx, between the tendons attached to 
that part. It receives terminal twigs of the middle sacral artery and 
minute filaments from the ganglion impar. It consists of an aggregation of 
grains or lobules, which in some instances remain separate one from 
another. These lobules are principally composed of thick- walled cavities of 
vesicular and tubular appearance, described by Luschka and subsequent 
writers as closed follicles filled with cellular contents, but recently demon- 
strated by Julius Arnold to be clumps of dilated and tortuous small arteries, 
with thickened muscular and epithelial coats. Nerve-cells are found scattered 
in the stroma of the organ. 

The coccygeal gland is a structure evidently of a similar nature to the ganglion 
intercaroticum, the principal differences apparently being, that the glomeruli of the 
ganglion intercaroticum are produced principally by the convolution and ramification 
of arterial twigs, while in the coccygeal gland there is dilation of the branches 
and thickening of their walls ; and that the nervous element 'is more developed 
in the intercarotid ganglion than in the coccygeal gland. Arnold, with Luschka, 
appears inclined to consider both structures as allied iu nature to the suprarenal cap- 
sules. According to Arnold, there is always a number of small grape-like appen- 
dages on the coccygeal part of the middle sacral artery, microscopic in size, but 
similar in nature to the lobules of which the coccygeal gland is composed. (Luschka, 
" Der Hirnanhang und die Steissdruse des Menschen." Berlin, 1860. Also "Anat. 
d. Menseh./' vol. ii. part 2, p. 187. Julius Arnold in Virchow's " Archiv," March, 
1865.) 

z z 



698 THE SYMPATHETIC NERVES. 



B. THE GREAT PLEXUSES OF THE SYMPATHETIC. 

Under this head may be included certain large plexuses of nerves placed 
further forwards in the visceral cavity than the gangliated cords, and 
furnishing branches to the viscera. The principal of these plexuses are the 
cardiac, the solar, and the hypogastric with the pelvic plexuses prolonged 
from it. They are composed of assemblages of nerves, or of nerves and 
ganglia, and from them smaller plexuses are derived. 

CARDIAC PLEXUS. 

This plexus receives the cardiac branches of the cervical ganglia and those 
of the pneumo-gastric nerves, and from it proceed the nerves which supply 
the heart, besides some oifsets which contribute to the nervous supply of 
the lungs. It lies upon the aorta and pulmonary artery, where these vessels 
are in contact, and in its network are distinguished two parts, the superficial 
aud the deep cardiac plexuses, the deep plexus being seen behind the vessels, 
and the superficial more in front, but both being closely connected. The 
branches pass from these plexuses chiefly forward in two bundles, accom- 
panying the coronary arteries. 

SUPERFICIAL CARDIAC PLEXUS. 

The superficial cardiac plexus lies in the concavity of the arch of the 
aorta, in front of the right branch of the pulmonary artery. In it the 
superficial or first cardiac nerve of the sympathetic of the left side termi- 
nates, either wholly or iu part, together with the lower cardiac branch of 
the left pneumo-gastric nerve, and in some cases also that of the right 
side. In the superficial plexus a small ganglion, the ganglion of Wrisberg, 
is frequently found at the point of union of the nerves. Besides ending in 
the anterior coronary plexus, the superficial carliac furnishes laterally 
filaments along the pulmonary artery to the anterior pulmonary plexus of 
the left side. 

DEEP CARDIAC PLEXUS. 

The deep cardiac plexus, much larger than the superficial one, is placed 
behind the arch of the aorta, between it and the end of the trachea, and 
above the point of division of the pulmonary artery. 

This plexus receives all the cardiac branches of the cervical ganglia of the 
sympathetic nerve, except the first or superficial cardiac nerve of the left 
side. It likewise receives the cardiac nerves furnished by the vagus and by 
the recurrent laryngeal branch of that nerve, with the exception of the 
left lower cardiac nerve. 

Of the branches from the right side of the plexus, the greater 
number descend in front of the right pulmonary artery, and join branches 
from the superficial part in the formation of the anterior coronary plexus, 
while the rest, passing behind the right pulmonary artery, are distributed 
to the right auricle of the heart, and a few filaments are continued 
into the posterior coronary plexus. 

On the left side, a few branches pass forwards by the side of the ductus 
arteriosus to join the superficial cardiac plexus ; but the great majority 
end in the posterior coronary plexus. 

The deep c.trdiac plexus sends filaments to the anterior pulmonary plexus 
on each bide. 



SOLAR PLEXUS. 699 

CORONARY PLEXUSES. The anterior coronary plexus, formed at first from the 
fibres of the superficial cardiac plexus, passes forwards between the aorta and pul- 
monary artery, and, having received an accession of fibres from the deep cardiac 
plexus, follows the course of the left or anterior coronary artery. 

The posterior coronary plexus, derived chiefly from the left part of the deep car- 
diac plexus, but joined by nerves from the right portion of that plexus, surrounding 
the branches of the right coronary artery accompany them to the back of the heart. 

Nervous filaments ramify in great number under the lining membrane of the 
heart. They are not so easily distinguished in man as in some animals. In the 
heart of the calf or lamb they are distinctly seen without dissection, running in lines 
which cross obliquely the muscular fibres. Remak was the first to observe that these 
branches are furnished with small ganglia, both on the surface and in the muscular 
substance. (Mailer's " Archiv," 1844.) 



SOLAR OR EPIGASTRIC PLEXUS. 

The solar or epigastric plexus, which is the largest of the prevertebral 
centres, is placed at the upper part of the abdomen, behind the stomach, and 
iii front of the aorta and the pillars of the diaphragm. Surrounding the 
origin of the coeliac axis and the upper mesenteric artery, it occupies the 
interval between the suprarenal bodies, and extends downwards as far as the 
pancreas. The plexus consists of nervous cords, with several ganglia of 
various sizes connected with them. The large splanchnic nerves on both sides, 
and some branches of the pneumo- gastric, terminate in it. The branches 
given off from it are very numerous, and accompany the arteries to the 
principal viscera of the abdomen, constituting so many secondary plexuses 
on the vessels. Thus diaphragmatic, coeliac, renal, mesenteric, and other 
plexuses are recognised, which follow the corresponding arteries. 

Semilunar ganglia. The solar plexus contains, as already mentioned, 
several ganglia ; and by the presence of these bodies, and their size, it is 
distinguished from the other prevertebral plexuses. The two principal 
ganglionic masses, named semtlttuor, though they have often little of the 
form the name implies, occupy the upper and outer part of the plexus, one 
on each side, and are placed close to the suprarenal bodies by the side of 
the coeliac and the superior mesenteric arteries. At the upper end, which 
is expanded, each ganglion receives the great splanchnic nerve. 

DIAPHRAGMATIC PLEXUS. The nerves (inferior diaphragmatic) composing this 
plexus are derived from the upper part of the semilunar ganglion, and are larger on 
the right than on the left side. Accompanying the arteries along the lower surface 
of the diaphragm, the nerves sink into the substance of the muscle. They furnish 
some filaments to the suprarenal body, and join with the spinal phrenic nerves. 

At the right side, on the under surface of the diaphragm, and near the suprarenal 
body, there is a small ganglion, ganglion diaphragmatic um, which marks the junc- 
tion between the phrenic nerves of the spinal and sympathetic systems. From this 
small ganglion filaments are distributed to the vena cava, the suprarenal body, and 
the hepatic plexus. On the left side the ganglion is wanting, but some filaments are 
prolonged to the hepatic plexus. 

SUPRARENAL PLEXUS. The suprarenal nerves issue from the solar plexus and the 
outer part of the semilunar ganglion, a few filaments being added from the diaphrag- 
matic nerve. They are short, but numerous in comparison with the size of the body 
which they supply : they enter the upper and inner parts of the suprarenal cap- 
sule. These nerves are continuous below with the renal plexus. The plexus is 
joined by branches from one of the splanchnic nerves, and presents a ganglion 
(g<ingl. splanchnico-suprarenale}, where it is connected with those branches. The. 
plexus and ganglion are smaller on the left than on the right side. 



700 



THE SYMPATHETIC NERVES. 



Fig. 455. 




ABDOMINAL PLEXUSES. 701 

Fig. 455. DIAGRAMMATIC VIEW OF THE SYMPATHETIC CORD OF THE RIGHT SIDE, WITH 
ITS PRINCIPAL GANGLIA, PLEXUSES, AND NERVES. 

This figure is repeated in illustration of the sympathetic uerves in the lower half of the 
body. 

c, superior cervical ganglion ; c', second or middle ; c", inferior : from each of these 
ganglia cardiac nerves (deep on this side) are seen descending to the cardiac plexus ; dl, 
placed immediately below the first dorsal sympathetic ganglion ; d 6, is opposite the 
sixth ; 1 1, first lumbar ganglion ; eg, the terminal or coccygeal ganglion ; pp, pharyugeal, 
aud, lower down, laryngeal plexus ; pi, posterior pulmonary plexus spreading from the 
pneumo-gastric on the back of the right bronchus ; ca, on the aorta, the cardiac plexus, 
towards which, in addition to the cardiac nerves from the three cervical sympathetic 
ganglia, other branches are seen descending from the pneumogastricand recurrent nerves ; 
co, right or posterior, and co', left or anterior coronary plexus ; o, ossophageal plexus in 
long meshes on the gullet ; sp, great splanchnic nerve formed by branches from the fifth, 
sixth, seventh, eighth, and ninth dorsal ganglia ; +, small splanchnic from the ninth 
and tenth ; + +, smallest or third splanchnic from the eleventh : the fir^t and second of 
these are shown joining the solar plexus, so; the third descending to the renal plexus, re; 
connecting branches between the solar plexus and the pneumo-gastric nerves are also re- 
presented ; pn', above the place where the right pneumo-gastric passes to the lower or 
posterior surface of the stomach ; pn", the left distributed on the anterior or upper surface 
of the cardiac portion of the organ : from the solar plexus large branches are seen sur- 
rounding the arteries of the cccliac axis, and descending to ins, the superior mesenteric 
plexus ; opposite to this is an indication of the suprarenal plexus ; below re (the renal 
plexus), the spermatic plexus is also indicated ; ao, on the front of the aorta, marks the 
aortic plexus, formed by nerves descending from the solar and superior mesenteric plexuses 
and from the lumbar ganglia ; mi, the inferior mesenteric plexus surrounding the cor- 
responding art* ry ; hy, hypogastric plexus placed between the common iliac vessels, 
connected above with the aortic plexus, receiving nerves from the lower lumbar ganglia, 
and dividing below into the right and left pelvic or inferior hypogastric plexuses ; pi, the 
right pelvic plexus ; from this the nerves descending are joined by those from the plexus 
on the superior heinorrhoidal vessel, mi', by sympathetic nerves from the sacral ganglia, 
and by numerous visceral nerves from the third and fourth sacral spinal nerves, and there 
are thus formed the rectal, vesical, and other plexuses, which ramify upon the viscera from 
behind forwards and from below upwards, as towards ir, and v, the i\ctum and bladder. 

RENAL PLEXUS. The nerves forming the renal plexus, fifteen or twenty in number, 
emanate for the most part from the outer part of the semilunar ganglion ; but 
some are added from the solar plexus and the aortic plexus. Moreover, filaments from 
the smallest splanchnic nerve, and occasionally from the other splanchnic nerves, 
terminate in the renal plexus. In their course along the renal artery, ganglia of dif- 
ferent sizes are formed on these nerves. Lastly, dividing with the branching of the 
vessel, the nerves follow the renal arteries into the substance of the kidney. On the 
right side some filaments are furnished to the vena cava, behind which the plexus 
passes with the renal artery ; and others go to form the spermatic plexus. 

SPERMATIC PLEXUS. This small plexus commences in the renal, but receives in its 
course along the spermatic artery an accession from the aortic plexus. Continuing 
downwards to the testis, the spermatic nerves are connected with others which 
accompany the vas defcrens and its artery from the pelvis. 

In the female, the plexus, like the artery, is distributed to the ovary and the 
uterus. 

CCELIAC PLEXUS. This plexus is of large size, and is derived from the fore part 
of the great epigastric plexus. It surrounds the coeliac axis in a kind of membra- 
nous sheath, and subdivides, with the artery, into coronary, hepatic, and splenic 
plexuses, the branches of which form communications corresponding with the arches 
of arterial anastomosis. The plexus receives offsets from one or more of the 
splanchnic nerves, and on the left side a branch from the pneumo-gastric nerve is 
continued into it. (Swan.) 

The coronary plexus is placed with its artery along the small curvature of the 
stomach, and unites with the nerves which accompany the pyloric artery, as well as 
with branches of the pneumo-gastric nerves. The nerves of this plexus enter the 
coats of the stomach, after running a short distance beneath the peritoneum. 

The hepatic plexus, the largest of the three divisions of the coeliac plexus, ascends 
with the hepatic vessels and the bile-duct, and ; entering the substance of the liver, 



702 THE SYMPATHETIC NERVES. 

ramifies on the branches of the vena portee and the hepatic artery. Offsets from the 
left pneu mo -gastric and diaphragmatic nerves join the hepatic plexus at the left 
side of the vessels. From this plexus filaments are furnished to the right supra- 
renal plexus, as well as other secondary plexuses which follow the branches of the 
hepatic artery. Thus there is a cystic plexus to the gall-bladder; and there are 
pylorie, gastro-epiploic, and gastro- duodenal plexuses, which unite with coronary, 
splenic, and mesenteric nerves. 

The splenic plexus, continued on the splenic artery and its branches into the 
substance of the spleen, is reinforced at its beginning by branches from the left semi- 
lunar ganglion, and by a filament from the right vagus nerve. It furnishes the left 
gastro-epiploic and pancreatic plexuses, which course along the corresponding branches 
of the splenic artery, and, like the vessals, are distributed to the stomach and 
pancreas. 

SUPERIOR MESENTERIC PLEXUS. The plexus accompanying the superior mesenteric 
artery, whiter in colour and firmer than either of the preceding offsets of the solar 
plexus, envelopes the artery in a membraniform sheath, and receives a prolongation 
from the junction of the right pneumo-gastric nerve with the cceliac plexus. Near 
the root of the artery, ganglionic masses (gangl. ineseraica) occur in connection with 
the nerves of this plexus. 

The offsets of the plexus are in name and distribution the same as the vessels. 
In their progress to the intestine some of the nerves quit the arteries which first sup- 
ported them, and are directed forwards in the intervals between the vessels. As they 
proceed, they divide, and unite with lateral branches, like the arteries, but without 
the same regularity : they finally pass upon the intestine along the line of attachment 
of the mesentery. 

THE AORTIC PLEXUS. 

The aortic or intermesentcric plexus, placed along the abdominal aorta, 
and occupying the interval between the origin of the superior and inferior 
mesenteric arteries, consists, for the most part, of two lateral portions, 
connected with the ^emilimar ganglia and renal plexuse?, which are extended 
on the sides of the aorta, and which meet in several larger communicating 
branches over the middle of that vessel. It is joined by branches from some 
of the lumbar ganglia, and presents not unfrequently one or more distinct 
ganglionic enlargements towards its centre. 

The aortic plexus furnishes the inferior mesenteric plexus and part of the 
spermatic, gives some filaments to the lower vena cava, and ends below in 
the hypogastric plexus. 

INFERIOR MESENTERIC PLEXUS. This plexus is derived principally from the left 
lateral part of the aortic plexus, and closely surrounds with a network the inferior 
meeenteric artery. It distributes nerves to the left or descending part and the 
sigmoid flexure of the colon, and assists in supplying the rectum. The nerves of this 
plexus, like those of the superior mesenteric plexus, are firm in texture, and of a 
whitish colour. 

The highest branches (those on the left colic artery) are connected with the last 
branches (middle colic) of the superior mesenteric plexus, while others in the pelvis 
unite with offsets derived from the pelvic plexus. 

HYPOGASTRIC PLEXUS. 

The hypogastric plexus, the assemblage of nerves destined for the supply 
of the viscera of the pelvis, lies invested in a sheath of dense connective 
tissue, in the interval between the tyvo common iliac arteries. It is formed 
by eight or ten nerves on each side, which descend from the aortic plexus, 
receiving considerable branches from the lumbar ganglia, and, after crossing 
the common iliac artery, interlace in tho form of a flat plexiform mass 
placed in front of the lowest lumbar vertebra. The plexus contains no 



HYPOGASTRIC AND PELVIC PLEXUSES. 703 

distinct ganglia. At the lower end it divides into two parts, which are 
directed forwards, one to each side of the pelvic viscera, and form the pelvic 
plexuses. 



PELVIC PLEXUS. 

The pelvic or inferior hypogastric plexuses, one on each side, are placed in 
the lower part of the pelvic cavity by the side of the rectum, and of the 
vagina in the female. The nerves, prolonged from the hypogastric plexus, 
enter into repeated communications as they descend, and form at the points 
of connection small knots, which contain a little gangliouic matter. After 
descending some way, they become united with branches of the spinal 
nerves, as well as with a few offsets of the sacral ganglia, and the union of 
all constitutes the pelvic plexus. The spinal branches, which enter into 
the plexus, are furnished from the third and fourth sacral nerves, especially 
the third ; and filaments are likewise added from the first and second 
sacral nerves. Small ganglia are formed at the places of union of the spinal 
nerves, as well as elsewhere in the plexus (plexus gangliosus Tiedemann). 

From the plexus so constituted numerous nerves are distributed to the 
pelvic viscera. They correspond with the branches of the internal iliac 
artery, and vary with the sex ; thus, besides haemorrhoidal and vesical 
nerves, which are common to both sexes, there are nerves special to 
each : namely in the male, for the prostate, vesicula seminalis, and vas 
deferens ; in the female, for the vagina, uterus, ovary, and Fallopian tube. 

The nerves distributed to the urinary bladder and the vagina contain a 
larger proportion of spinal nerves than those furnished to the other pelvic 
viscera. 

INFERIOR ILEMORRHOIDAL NERVES. These slender nerves proceed 
from the back part of the pelvic plexus. They join with the nerves 
(superior hsemorrhoidal) which descend with the inferior mesenteric artery, 
and penetrate the coats of the rectum. 

VESICAL PLEXUS. The nerves of the urinary bladder are very numerous. 
They are directed from the anterior part of the pelvic plexus to the side 
and lower part of the bladder. At first, these nerves accompany the vesical 
blood-vessels, but afterwards they leave the vessels, and subdivide into 
minute branches before perforating the muscular coat of the organ. 
Secondary plexuses are given in the male to the ras deferens and the 
vesicula seminalis. 

The nerves of the vas deferens ramify round that tube, and communicate 
in the spermatic cord with the nerves of the spermatic plexus. Those 
furnished to the vesicula seminalis form an interlacement on the vesicula, 
and some branches penetrate its substance. Other filaments from the 
prostatic nerves reach the same structure. 

PROSTATIC PLEXUS. The nerves of this plexus are of considerable size, 
and pass onwards between the prostate gland and the levator ani. Some are 
furnished to the prostate and to the vesicula seminalis ; and the plexus is 
then continued forwards to supply the erectile substance of the penis, where 
its nerves are named " cavernous." 

Cavernous nerves of the penis. These are very slender, and difficult to 
dissect. Continuing from, the prostatic plexus they pass onwards, beneath 
the arch of the pubes, and through the muscular structure connected with 
the membranous part of the urethra, to the dorsum of the penis. At ths 



704 THE SYMPATHETIC NERVES. 

anterior margin of the levator ani muscle the cavernous nerves are joined 
by some short filaments from the pudic nerve. After distributing twigs to 
the forepart of the prostate, these nerves divide into branches for the erectile 
substance of the penis, as follows : 

Small cavernous nerves (Mtiller), which perforate the fibrous covering of 
the corpus cavernosum near the root of the penis, and end in the erectile 
substance. 

The large cavernous nerve, which extends forward on the dorsum of the 
penis, and dividing, gives filaments that penetrate the corpus cavernosum, 
and pass with or near the cavernous artery (art. profunda penis). As it 
continues onwards, this nerve joins with the dorsal branch of the pudic 
nerve about the middle of the penis, and is distributed to the corpus 
cavernosum. Branches from, the foregoing nerves reach the corpus spongi- 
osum urethrse. (Miiller, " Ueber die organischen Nerven der erectilen 
marinlichen Geschlechtsorgane," <fec. Berlin, 1836.) 

NERVES OF THE OVARY. The ovary is supplied chiefly from the plexus 
prolonged on the ovarian artery from the abdomen ; but it receives another 
offset from the uterine nerves. 

VAGINAL PLEXUS. The nerves furnished to the vagina leave the lower 
part of the pelvic plexus that part with which the spinal nerves are more 
particularly combined. They are distributed to the vagina without pre- 
viously entering into a plexiform arrangement ; and they end in the erectile 
tissue on the lower and anterior part, and in the mucous membrane. 

NERVES OF THE UTERUS. These nerves are given more immediately 
from the lateral fasciculus prolonged to the pelvic plexus from the hypo- 
gastric plexus, above the point of connection with the sacral nerves. 
Separating opposite the neck of the uterus, they are directed upwards with 
the blood-vessels along the side of this organ, between the layers of its 
broad ligament. Some very slender filaments form round the arteries a 
plexus, in which minute ganglia are found scattered at intervals, and these 
nerves continue their course in the substance of the organ in connection 
with the blood-vessels. But the larger part of the nerves soon leave the 
vessels ; and after dividing repeatedly, without communicating with each 
other and without forming any gangliform enlargements, sink into the sub- 
stance of the uterus, penetrating for the most part its neck and the lower 
part of its body. One branch, continued directly from the common hypo- 
gastric plexus, reaches the body of the uterus above the rest ; and a nerve 
from the same source ascends to the Fallopian tube. Lastly, the ftindus of 
the uterus often receives a branch from the ovarian nerve. (Fr. Tiede- 
mann, Tab. Nerv. Uteri, Heidelberg, 1822 ; Robert Lee, in Phil. Trans., 
1841, 1842, 1846, and 1849; and Snow Beck, in Phil. Trans., 1846, 
part ii.) 

The nerves of the gravid uterus have been frequently investigated, 
with a view to discover if they become enlarged along with the increase 
in size of the organ. It is ascertained that the increase which takes place 
is confined, for the most part, to thickening of the fibrous envelopes of 
the nerves ; but it appears also, from the researches of Kilian, that fibres 
furnished with a medullary sheath, which in the unimpregnated state of the 
uterus lose that sheath as they proceed to their distribution, in the im- 
pregnated condition of the uterus continue to be surrounded with it as 
they run between the muscular fibres. (Farre, in Supplement of Cyclopaedia 
of Anat. and Phys., " Uterus and Appendages.") 



ORGANS OF THE SENSES. THE EYE. 705 



IY. ORGANS OF THE SENSES. 

In this place it is intended to describe the organs of sight, hearing and 
smelling, which, considered with reference to their anatomy and develop- 
ment, are regarded as the higher organs of special sense. The description 
of the organ of touch is given along with the skin in the histological part 
of the work, and that of the organ of taste along with the descriptive 
anatomy of the digestive system. 

THE EYE. 

The organ of vision, strictly speaking, consists only of the ball or globe 
of the eye, a spheroidal structure enclosed by strong membranous coverings, 
receiving the optic nerve posteriorly, and containing the sensitive termina- 
tions of that nerve, together with a series of transparent media, which con- 
stitute an optical instrument of variable focus, through which the rays of light 
are transmitted to the sensitive part, and so brought into focus as to form 
upon it a distinct inverted image of the objects from which they proceed. 
Eut there are likewise various structures external to the eyeball which con- 
tribute to the production of perfect vision, such as the straight and oblique 
muscles by which the eyeball is moved in different directions, and the various 
supporting and protective structures known as appendages of the eye (tuta- 
mina oculi), including the eyebrows, eyelids, and conjunctiva, and the lachry- 
mal apparatus. 

APPENDAGES OP THE EYE. 

THE EYELII>S AND CONJUNCTIVA. 

The eyelids (palpebrse) are moveable folds of integument, strengthened 
toward their margins by a thin lamina of cartilage. The mucous membrane, 
which lines their inner surface, and which is reflected thence in the form of 
a pellucid covering on the surface of the eyeball, is named membrana con- 
junctiva. 

The upper lid is larger and more moveable than the lower : the trans- 
parent part of the globe is covered by it when the eye is closed ; and the eye 
is opened chiefly by the elevation of this lid by a muscle (levator palpebrse) 
devoted exclusively to this purpose. The eyelids are joined at the outer and 
inner angles (canthi) of the eye. The interval between the angles, fissura 
palpebrarum; varies in length in different persons, and, according to its 
extent, the size of the globe being nearly the same, gives the appearance of 
a larger or a smaller eye. The greater part of the edge of each eyelid is flat- 
tened, but towards the inner angle it is rounded off for a short space, at the 
same time that it somewhat changes its direction ; and, where the two differ- 
ently formed parts join, there exists on each lid a slight conical elevation 
papitta lachrymalis, the apex of which is pierced by the aperture or punctum 
of the corresponding lachrymal canalicule. 

In the greater part of their extent the lids are applied to the surface of the 
eyeball ; but at the inner canthus, opposite the puncta lachrymalia, there 
intervenes a vertical fold of conjunctiva, the plica semilunaris, resting on 
the eyeball ; while, occupying the recess of the angle internal to the border 
of this fold, is a spongy-looking reddish elevation, formed by a group of 

3 A 



706 



THE EYE. 



glandular follicles, and named the caruncula lachrymalis. The plica 
semilunaris is the rudiment of the third eyelid (rneinbrana nictitans) found 
in some animals. 

Structure of the lids. The skiu covering the eyelids is thin and delicate; 
and at the line of the eyelashes, altered in its character, it joins the conjunc- 
tival mucous membrane which lines the inner surface of the lids. Beneath 
the skin, and between it and the conjunctiva, the following structures are 
successively met with, viz. : The fibres of the orbicularis muscle ; loose 
connective tissue ; the tarsal cartilages, together with a thin fibrous mem- 
brane, the palpebral ligament, which attaches them to the margin of the 
orbit ; and, finally, the Meibomian glands. In the upper eyelid there is, in 
addition, the insertion of the levator palpebrse superioris, in the form of a 
fibrous expansion fixed, to the anterior surface of the tarsal cartilage. 

Fig. 456. 




Fig. 456. VERTICAL SECTION OF THE LEFT ORBIT AND ITS CONTENTS. 

The section has been carried through the middle of the optic foramen and optic nerve 
obliquely as far as the back of the eyeball, and thence forward through the eyeball, 
eyelids, &c., in an antero-posterior direction, a, the frontal bone; 6, the superior 
maxillary bone; c, the eyebrow with the orbicularis palpebrarum, integument, &c. , 
divided ; d, the upper, and d, the lower eyelid, partially open, showing the section of the 
tarsal cartilages and other component parts, the eyelashes, &c. ; e, e, the reflection of 
the conjunctiva from the upper and lower eyelids to the surface of the eyeball ; /, the 
levator palpebraa superioris muscle; <?, the upper, #', the lower rectus muscle; h, the 
inferior oblique muscle divided ; 1, 1, the optic nerve divided in its sheath ; 2, the 
cornea ; 2', the sclerotic ; 3, the aqueous chamber ; 4, the crystalline lens ; 5, the 
centre of the vitreous humour. 

The fibres of the orbicularis muscle are closely adherent to the skin by fine 
connective tissue, entirely devoid of fat. A marginal fasciculus of its fibres 
has been found within the line of the eyelashes, separated by the bulbs of 
the lashes from the other fibres, and constituting the ciliary muscle of Riolan. 
The fibres of the orbicular muscle, while adherent to the skin, glide loosely 
on the tarsal cartilages. 

The tarsal cartilages (tarsi) are two thin elongated plates of cartilages of 
the yellow kind placed one in each lid, and serving to give shape and firm- 
ness to those parts. The upper cartilage, the larger, is half oval in form, 



THE EYELIDS AND CONJUNCTIVA. 



707 



being broader near the centre and narrowing towards the angles of the lids. 
The lower is thinner, much narrower, and more nearly of an uniform breadth 
throughout. The free or ciliary edge of the cartilages, which is straight, is 
thicker than any other part. At the inner canthus the cartilages are fixed 
by the fibrous slips of the tendo palpebrarum (p. 172) ; and at the outer 
angle they are attached to the malar bone by a fibrous band belonging to the 
palpebral ligament, and named the external tarsal ligament. 

The palpebral ligament is a fibrous membrane placed beneath the orbicularis 
muscle, attached peripherally to the margin of the orbit, and internally to 
the tarsal cartilages near the inner free edge. The membrane is thickest at 
the outer part of the orbit. 

Meibomian glands. On the ocular surface of each lid are seen from twenty 
to thirty parallel vertical lines of yellow granules, lying immediately under 
the conjunctiva! mucous membrane. They are compound sebacious follicles, 



Fig. 457. 




Fig. 457. MEIBOMIAN GLANDS, 
LACHRYMAL GLAND, &c., AS SKEN 
FROM THE DEEP SURFACE OF THE 
EYELIDS OF THE LEFT SIDE. 

a, palpehral conjunctiva ; 1, 
lachrymal gland ; 2, openings of 
seven or eight glandular ducts ; 3, 
upper and lower puncta lachry- 
inalia ; 6, 6, shut ends of the 
upper and lower Meihomian glands, 
of which the openings are indicated 
along the margins of the eyelids. 



embedded in grooves at the 

back of the taral cartilages ; 

and they open on the free 

margin of the lids by minute 

orifices, generally as many in 

number as the lines of follicles 

themselves. These glands consist of nearly straight excretory tubes, each 

of which is closed at the end, and has numerous small coecal appendages 

projecting from its sides. The tubes are lined by mucous membrane, oil 

the surface of which is a layer of scaly or pavement epithelium cells. 

According to Heinrich Miiller there is likewise a layer of unstriped muscular fibre 
contained in each eyelid ; that of the upper lid arising from the under surface of the 
levator palpebrse, that of the lower lid arising from the neighbourhood of the inferior 
oblique muscle, and each being inserted near the margin of the tarsal cartilage. It 
may also be mentioned in this place that the same writer describes a layer of unstriped 
muscle crossing the spheno-maxillary fissure, corresponding to a more largely developed 
layer found in the extensive aponeurotic part of the orbital wall of various mammalia. 
This set of fibres has been more particularly described by Turner (H. Miiller, in 
Zeitschr. f. Wiss. Zool. 1858, p. 541; W. Turner, in Nat. Hist. Eev. 1862, p. 106). 

The eyelashes (cilia) are strong short curved hsirs, arranged in two or 
more rows along the margin of the lids, at the line of uni >n between the 
skin and the conjunctival mucous membrane. The lashes of the upper lid, 
more numerous and longer than the lower, have the convexity of their curve 
directed downwards and forwards ; whilst those of the lower lid are arched 
in the opposite direction. Near the inner canthus these hairs are weaker 
and more scattered. 

3 A 2 



708 THE EYE. 

Structure of the conjunctiva. The conjunctiva consists of the palpebral 
part, along with which may be grouped the plica semilunaris and caruncula 
lachrymalis, and of the ocular part or conjunctiva bulbi, in which may be 
distinguished the sclerotic and corneal portions : each of these several parts 
presents peculiar and distinctive characters. The epithelium is stratified and 
thick ; the cells of the superficial strata scaly, delicate, and each with a 
distinct nucleus. 

The palpebral portion of the conjunctiva is opaque and red, is thicker and 
more vascular than auy other part of the membrane, and presents numerous 
fine papillae freely supplied with nerves. At the margins of the lids 
the palpebral conjunctiva enters the ducts of the Meibomian glands ; 
through the pun eta lachrymalia it passes into the canaliculi, and is con- 
tinuous with the lining membrane of the lachrymal sac ; and it is prolonged 
into the orifices of the ducts of the lachrymal gland. 

The sclerotic portion of the conjunctiva, changing its character at the line 
of reflection from the eyelids, becomes thinner, and loses its papillary 
structure : it is loosely connected to the eyeball by submucous tissue. It is 
also transparent and nearly colourless, but a few scattered branches of blood- 
vessels are generally visible on it in the healthy condition, and under the 
influence of inflammatory congestion a copious network of vessels very irre- 
gularly disposed comes into view. This network is derived from the palpebral 
and lachrymal arteries. It may be easily made to glide loosely on the sur- 
face of the eyeball by pressing the eyelid against it. But another set of 
vessels likewise exists on the surface of the sclerotic, and may be brought 
into view by congestion. The position of this set is entirely sub-conjunc- 
tival, adherent to the sclerotic coat ; they are less tortuous than the conjunc- 
tival set, and are derived from the muscular and anterior ciliary branches of 
the ophthalmic artery : they remain immoveable on pressure of the eyelid. 
They dip into the sclerotic near the cornea, and appear to unite with a more 
deeply connected minute network disposed in closely set straight lines, 
radiating from the margin of the cornea, and the gorged condition of which 
is well known to ophthalmic surgeons as characteristic of sclerotitis. 

The corneal conjunctiva consists almost entirely of epithelium, any under- 
lying membrane being extremely thin, transparent, and adherent to the 
anterior elastic layer of the cornea, in connection with which it will be again 
referred to. Vessels lie between it and the cornea, and form a circle of 
anastomotic capillary loops around the circumference. This plexus of 
vessels extends farther inwards in the foetus. 

A well developed network of lymphatics exists throughout the sclerotic and palpebral 
portions of the conjunctiva ; but at the margin of the cornea a sudden diminution 
takes place in the size of the meshes and diameter of the vessels. Of the network 
referred to, only a narrow circle ~th of an inch in diameter exists on the corneal 
conjunctiva, and this circle has a well defined inner margin within which no lym- 
phatics exist (Teichmann). 

The nerves in the membrane, as far as the cornea, seem to have the same arrange- 
ment as in the skin in general. 

In the submucous tissue of the eyelids there are small follicular glands spread over 
the whole surface of the conjunctiva palpebrarum, and in the vicinity of the reflection 
of the conjunctiva upon the eyeball a set of larger more complex glands of a racemose 
structure, somewhat similar to that of the lachrymal gland (Sappey, C. aud W. 
Krause). 

Closed follicles have also been observed in the conjunctiva by Bruch, and, after 
him, by other observers. 



LACHRYMAL GLANDS AND CANALS. 709 

THE LACHRYMAL APPARATUS. 

The parts which constitute the lachrymal apparatus are the following, 
viz. : The gland by \\hich the tears are secreted, situated at the upper and 
outer side of the orbit, together with its excretory ducts ; the two canals 
into which the fluid is received near the inner angle ; and the sac wuh the 
nasal duct continued from it, through which the teard pass into the inferior 
meat us of the nose. 

The lachrymal gland, an oblong flattened body, about the size of a small 
almond, is placed in the upper and outer part of the orbit, a little behind 
the anterior margin. The upper surface of the gland, convex, is lodged in a 
slight depression in the orbital plate of the frontal bone, to the periosteum 
of which it adheres by fibrous bands ; the lower surface is adapted to the 
convexity of the eyeball, and is in contact with the upper and the outer 
recti muscles. The fore part of the gland, separated from the rest by a 
slight depression, and sometimes described as a second lobe, or as a distinct 
gland, is closely adherent to the back of the upper eyelid, and is covered on 
the ocular surface only by a reflection of the conjunctiva. The glandular 
ducts, usually from six to eight in number, are very small, and emerge from 
the thinner portion of the gland. After running obliquely under the mucous 
membrane, and separating at the same time from each other, they open in a 
row by separate orifices, the greater number in the fold above the outer 
cauthus, and two of them (Hyrtl) in the fold below. 

Fig. 458. FRONT OP THE LEFT EYELIDS, p. ._ 

WITH THE LACHRYMAL CANALS AND NA- *>' 

SAL DUCT EXPOSED. 

1,1, upper and lower lachrymal canals, 
showing towards the eyelids the narrow 
bent portions and the puncta lachrymal ia ; 
2, lachrymal sac ; 3, the lower parjb of the 
uasal duct ; 4, plica semilunaris ; 5, ca- 
runcula lachrymalis. 




Lachrymal canals. On the mar- 
gin of each lid, near the inuer 
angle, and in front of the fold of 
membrane called plica semilunaris, 
is a small elevation (papilla lachry- 
malis), already described. Each 
papilla is perforated by a small 
aperture, punctum lachrymale ; and 

at these apertures commence two small canals, canaliculi, which convey 
the tears from the eye to the lachrymal sac. The upper canal is rather 
the smaller and longer of the two : it first ascends from the punctum ; then 
makes a sudden bend, and is directed inwards and downwards to join the 
lachrymal sac. The lower canal descends from the corresponding punctum ; 
and soon changing its direction like the upper one, takes a nearly horizontal 
course inwards. Both canals are dilated where they are bent. In some 
cases they unite near the end to form a short common trunk ; more 
commonly they open separately, but close together, into the sac. 

The lachrymal sac and nasal duct constitute together the passage by which 
the tears are conveyed from the lachrymal canals to the cavity of the nose. 



710 THE EYE. 

The lachrymal sac, the upper dilated portion of the passage, is situated at 
the side of the nose, near the inner canthus of the eye, and lies embedded 
in a deep groove in the lachrymal and upper maxillary bones. It is of an oval 
form ; the upper end closed and rounded, and the lower end gradually 
narrowiug somewhat into the nasal duct. On the outer side, and a little in 
front, it receives the lachrymal canals ; and here it is covered by the tendo 
palpebrarum, and by some of the inner fibres of the orbicular muscle of the 
lids; while on its inner or posterior. surface the tensor tarsi muscle is placed. 
The sac is composed of fibrous and elastic tissues, adhering closely to the 
bones above mentioned, and strengthened by fibrous processes sent from the 
tendo palpebrarum, which crosses a little above its middle. The inner sur- 
face is lined by a reddish mucous membrane, which is continuous through 
the canaliculi with the conjunctiva, and through the nasal duct with the 
mucous membrane of the nose. 

The nasal duct (ductus ad nasum), about six or seven lines in length, 
grooving the upper maxillary bone, descends to the fore part of the lower 
meatus of the nose, the osseous canal being completed by the ungual and 
lower turbiuated bones. A tube of fibrous membrane, continuous with the 
lachrymal sac, adheres to the parietes of this canal, and is lined by mucous 
membrane, which, at the opening into the nose, is often arranged in the 
form of an imperfect valve. The nasal duct is rather narrower in the middle 
than at either end ; its direction is not quite vertical, but inclined slightly 
outwards and backwards. 

The mucous membrane in the canaliculi possesses a laminar epithelium, 
but in the nasal sac and duct a ciliated epithelium as in the nose. 

Various valves have been described in connection with the lachrymal sac and canals. 
One, the valve of Hasner, is formed by the mucous membrane of the nose overhanging 
the inferior orifice of the nasal duct, and has had imputed to it the function of pre- 
venting entrance of foreign matters in violent expiratory movements; but the 
disposition of the mucous membrane at this orifice appears to be subject to some 
variation. Another fold, the valve of Huschke, placed at the deep orifice of the canali- 
culi, is supposed by some to prevent the return of the tears from the sac into those 
tubes, but by others, it is declared to be inconstant, and insufficient, even when found, 
to close the orifice. A third fold, the valve of Foltz, is described as forming a projection 
inwards on one side of the vertical part of each canaliculus, near the punctual 
lachrymale, and as being sufficient to close the tube when it is flattened by the 
pressure of the fibres of the orbicularis and tensor tarsi muscles as in winking. The 
experiments of Foltz on rabbits go to prove that the punctum lachrymale having been 
turned backwards towards the eye in winking, and the canaliculus being compressed 
by the muscles, as soon as the pressure is removed the canaliculus resumes its open 
form, and so sucks in tears which by the next compression in winking are forced 
onwards into the lachrymal sac ; and also, that when the muscles are paralysed, the 
canaliculi cease to carry away the tears. See review of Foltz 's paper in Dublin 
Quarterly Journal, Feby. 1863; also, Hyrtl, Topogr. Anatomic. 



THE GLOBE OF THE EYE. 

The globe or ball of the eye is a composite structure of an irregularly 
spheroidal form, placed in the fore part of the orbital cavity, and receiving 
the thick stem of the optic nerve behind. The recti and obliqui muscles 
closely surround the greater part of the eyeball, and are capable of changing 
its position within certain limits : the lids, with the plica semilunaris and 
caruncle, are in contact with its covering of conjunctiva in front ; and 
behind it is supported by a quantity of loose fat and connective tissue. 



THE EYEBALL. THE SCLEFxOTIC COAT. 711 

The eyeball, when viewed in profile, is found to be composed of segments 
of two spheres, of which the anterior is the smaller and more prominent : 
the segment of the larger posterior opaque sphere corresponds with the limit 
of the sclerotic coat, and the translucent portion of the smaller sphere with 
that of the cornea. 

From before backwards the ball measures about nine-tenths of an inch, 
and its transverse diameter exceeds this measurement by about a line. 

Except when directed towards near objects, the axes of the eyes are nearly 
parallel ; the optic nerves, on the contrary, diverge considerably from one 
another, and each nerve enters the corresponding eye about a tenth of an 
inch to the inner or nasal side of the axis of the globe. 

The eyeball is composed of several investing membranes, concentrically 
arranged, and of certain fluid and solid paits contained within them. The 
membranes are three in number, with the following designations and general 
structure : An external fibrous covering, named sclerotic and cornea ; a 
middle vascular, pigmentary, and in part also muscular membrane, the choroid 
and the iris ; and an iuternal nervous stratum, the retina. The enclosed 
refracting media, three in number, are the aqueous humour, the vitreous body, 
and the lens with its capsule. 

Around the eyeball there is an adventitious tunic of fascia, tunica 
vaginalis oculij or capsule of Tenon, which is perforated by the tendons of 
the recti and obliqui muscles, and connected with the sclerotic by merely the 
most delicate connective tissue. This capsule separates the eye-ball from the 
orbital fat, and enables it to glide freely in its movements. (See, for details, 
Richet, Traite d'Anatomie Medico-Chirurgicale ; and O'Ferrall, in Dublin 
Quart. Journ. Med. Science, July, 1841.) 



EXTERNAL COAT OF THE EYEBALL. 

The external investing membrane, which forms a complete covering for the 
ball, consists of two parts of different appearance and structure. Of these 
the hinder part, much the largest, is opaque and densely fibrous, and is 
named the sclerotic coat, while the anterior smaller segment is transparent, 
and is named the cornea. 

THE SCLEROTIC COAT. 

The sclerotic (cornea opaca), the tunic of the eye on which the mainte- 
nance of the form of the greater part of the organ chiefly depends, is a 
strong, opaque, unyielding, fibrous structure. The membrane covers about 
five-sixths of the eye-ball, and is pierced behind by the optic nerve. The 
outer surface is white and smooth, except where the tendons of the recti and 
obliqui muscles are inserted into it. The inner surface is of a light brown 
colour, and rough from the presence of a delicate connective tissue (membrana 
fusca), through which branches of the ciliary vessels and nerves cross 
obliquely. The sclerotic is thickest at the back part of the eye, and thinnest 
at about a quarter of an inch from the cornea : at the junction with the 
cornea, it is again somewhat thickened. The optic nerve pierces this coat 
about one-tenth of an inch internal to the axis of the ball, and the opening 
is somewhat smaller at the inner than at the outer surface of the coat. The 
fibrous sheath of the nerve, together with the membranous processes which 
separate the funiculi of its fibres, blend with the sclerotic at the margin of 
the aperture : in consequence of this arrangement, when the neive is cut off 



712 



THE EYE. 



close to the eye-ball, the funiculi are seen to enter by a group of pores ; and 
to the part of the sclerotic thus perforated the name of lamina cribtosa is 
sometimes given. Around this cribrous opening are smaller apertures for 
vessels and nerves. 

Fig. 459. 




Fig. 459. VIEW OP THE LOWER HALF OP THE RIGHT ADULT HUMAN EYE, DIVIDED 

HORIZONTALLY THROUGH THE MIDDLE. 

The specimen from which this outline is taken was obtained by dividing the eye of a 
man of about forty years of age in the frozen state. It was carefully compared with 
other specimens obtained in a similar manner ; and in the drawing averages have been 
given in any particulars in which differences among them presented themselves. 

1, the cornea ; 1', its conjunctival layer ; 2, the sclerotic ; 2', sheath of the optic 
nerve passing into the sclerotic ; 3, external or vascular layer of the choroid ; 3', its 
internal pigmental layer ; 4, ciliary muscle, its radiating portion ; 4', cut fibres of the 
circular portion ; 5, ciliary fold or process ; 6, placed in the posterior division of the 
aqueous chamber, in front of the suspensory ligament of the lens ; 7, the iris (outer side) ; 
7', the smaller inner side ; 8, placed on the divided optic nerve, points to the arteria 
centralis retinae ; 8', colliculus or eminence at the passage of the optic nerve into the 



THE SCLEROTIC COAT. 713 

retina ; 8", fovea centralis retinae ; r, the nervous layer of the retina ; /, the bacillar 
layer; 9, ora serrata at the commencement of the ciliary part of the retina ; 10, canal 
of Petit; 11, anterior division of the aqueous chamber in front of the pupil; 12, the 
crystalline lens, within its capsule ; 13, the vitreous humour ; a, a, a, parts of a 
dotted line in the axis of the eye; b, b, b, b, a line in the transverse diameter. It will 
be observed that from the pupil being placed nearer the inner side the axis of the eye-ball 
a, a, does not pass exactly through the centre of the pupil, and that this line falls a 
little to the inner side of the fovea centralis. The following letters indicate the centres 
of the curvatures of the different surfaces ; assuming them to be nearly spherical, viz. : 
c a, anterior surface of the cornea ; c p, posterior surface ; I a, anterior surface of the 
lens ; I p, posterior surface ; s c p, posterior surface of the sclerotic ; r a, anterior surface 
of the retina. 

In connection with this figure the following average dimensions of the parts of the 
adult eye in fractions of an English inch may be stated : 

Transverse diameter of the eyeball . . . . . . . 1* 

Vertical diameter (Krause) ......... 0*96 

Antero-posterior diameter . . . . . . . . . 0'96 

Diameter of the optic nerve with its sheath . . . . . . 0'16 

Diameter of the nervous part at its passage through the choroid membrane 0*09 

Greatest thickness of the sclerotic, choroid, and retina together . . 0'08 

Greatest thickness of the sclerotic posteriorly 0'05 

Smallest thickness at the sides and in front ...... 0'025 

Greatest thickness of the cornea 0'055 

Distance from the middle of the posterior surface of the cornea to the 

front of the lens 0'07 

Antero-posterior diameter of the lens . . . . . . . 0'19 

Transverse ditto 0'35 

Greatest thickness of the ciliary muscle and ciliary processes together . . 0'06 

Greatest thickness of the ciliary muscle ...... 0'035 

Thickness of the iris 0'015 

Length of the radius of curvature of the anterior surface of the cornea 

(regarding it approximately as spherical) .0 '305 

Radius of the posterior surface 0'275 

Radius of curvature of the anterior surface of the lens . . . . 0'36 

Radius of the posterior surface . . . . . . . . 0'21 

Approximate length of the radius of curvature of the outer surface in the 

posterior half of the retina . . (H85 

Approximate radius of curvature of the external surface of the posterior 

part of the sclerotic coat ......... 0*5 

Distance of the middle of the posterior surface of the lens from the 

middle of the retina 0'575 

Distance between the centre of the spot of entrance of the optic nerve and 

the middle of the fovea centralis retinae 0*14 

Diameter of the base of the cornea ....... 0'48 

Diameter of the base of the iris transversely . . . . . . 0'45 

Diameter of the base of the iris vertically ...... 0*43 

Diameter of the pupil . . . . 0'14 

STRUCTURE. The sclerotic coat is formed of connective tissue, and yields 
gelatine on boiling. Its fibres are combined with fine elastic tissue, and 
with fusiform and stellate nucleated cells, and are aggregated into bundles, 
which are disposed in layers both longitudinally and transversely, the longi- 
tudinal arrangement being most marked at the surfaces. These layers com- 
municate at intervals, and the sclerotic presents a ramified and laminar 
appearance on a vertical section. 

A few blood-vessels permeate the fibrous texture in the form of a net- work 
of the smallest capillaries with very wide meshes ; and in the neighbourhood 
of the cornea a ring of greater vascularity exists, which has been already 
noticed in the description of the sclerotic conjunctiva. The existence of 
nerves in the sclerotic has not yet been allowed by all anatomists. 



714 



THE EYE. 



THE CORNEA. 

The cornea (cornea pellucida), the transparent fore parb of the external 
coat, admits light into the interior of the ball. It is neaily circular in 
shape, and its arc extends to about one-sixth of the circumference of the 
whole globe ; it is occasionally widest in the transverse direction. Being 
of a curvature of a smaller radius than the sclerotic, it projects forwards 
beyond the general surface of curvature of that membrane, somewhat like 
the glass of a watch : the degree of its curve varies, however, in different 
persons, and at different periods of life in the same person, being more 
prominent in youth and flattened in advanced age. Its thickness is in 
general nearly the same throughout, viz., from ~ to ^ of an inch, except- 
ing towards the outer margin, where it becomes somewhat thinner. The 
posterior concave surface exceeds slightly in extent the anterior or convex, in 
consequence of the latter being encroached on by the opacity of the sclerotic. 



Fig. 460. 

A 



Fig. 461. 





Fig. 460. STRUCTURES OF THE CORNEA (after Bowman). A 5p, B & C, 30 

A, small portion of a vertical section of the cornea in the adult ; a, conjunctival 
epithelium ; 6, anterior elastic lamina ; c to d, fibrous laminae with nuclear bodies inter- 
spersed between them ; c, fibres shooting through some of these layers from the external 
elastic lamina ; d, posterior elastic lamina ; e, internal epithelium. B, epithelium of 
the membrane of Demours, as seen looking towards its surface. C, the same seen in 
section. 

Fig. 461. SMALL PORTIONS OP A VERTICAL SECTION OF THE CORNEA AT BIRTH 
(from Kolliker). 3 fJ 

The preparation has been treated with acetic acid. A, the anterior p.irt ; a, anterior 
elastic lamina ; b, layer of closely set granules (probably small cells) placed under the 
anterior elastic layer, with little fibrous structure ; c, developed fibrous tissue, with 
united connective-tissue corpuscles ; B, posterior part of the cornea ; c, as before ; d, 
posterior elastic layer. 



THE CORXEA. 715 

At its circumference the cornea joins the sclerotic part by continuity of tissue, 
but always so as to be overlapped by the opacity of that structure like a 
watch glass by the edge of the groove into which it is received. 

STRUCTURE. The cornea consists of a central thick fibrous part, the 
cornea proper, covered in front by the conjunctival epithelium and the ante- 
rior elastic lamina, and behind by the posterior elastic lamina or membrane 
of Demours. 

The cornea proper is a stratified structure, the constituent fibres of which, 
continuous externally with those of the opaque sclerotic, are soft and com- 
paratively indistinct, and between the strata of which are numerous delicate 
anastomosing nucleated cells, of fusiform appearance as seen in vertical sec- 
tions, but expanded in the direction of the laminae, and presenting in sections 
parallel to the surface a stellate appearance. The strata, about sixty in 
number, at a given spot (Bowman),* maintain frequent communications with 
contiguous layers, so that they can be detached only for a very short dis- 
tance : in consequence of this stratified composition the cornea may be 
penetrated or torn most readily in the direction of the supposed laminse. 
The transparency of the cornea is impaired by derangement of the relative 
position, or by approximation of the strata to each other. The cornea 
proper is permeable to fluid, and affords chondrin, not gelatine, on boiling 
(J. Miiller). 

There have been observed by v. Recklinghausen in the cornea of the frog, when 
examined in a chamber of liquid connected with the microscope, not only a rich net- 
work of anastomosing cells, but other cells also which change both their form and 
position by means of processes thrown out from and disappearing again into their sub- 
stance, like the pseudopods of amoebae. (Virchow's Archiv, Vol. 28, p. 157). 

According to Henle, the anastomosing cells of the cornea are mere spaces devoid of 
any walls distinct from the surrounding matrix, and are the only interlaminar spaces 
naturally existing. (Systematise-he Anatomic, Vol. ii. p. 599). 

The membranes investing the fibrous part of the cornea before and behind 
are both of them structureless, with epithelium on their free surface. 

The anterior elastic lamina (Bowman) is a transparent glassy stratum with- 
out recognised texture, from ^^^th to -y^^th of an inch thick, and not 
rendered opaque by acids. From the surface resting on the fibrous strata of 
the cornea, a few fine threads are prolonged in a slanting direction, and are 
lost among the more superficial of those strata : their action is supposed to 
be to keep the membrane tied down smoothly to the cornea. The epithelium 
on the front of this lamina is stratified, the superficial cells being flat, and 
the main thickness formed of three or four layers of rounded cells, the deepest 
of which are vertically elongated, so as to be nearly twice as long as broad. 

It is right to mention that this epithelium in the horse, the ox, and the sheep, has a 
much more remarkable appearance than in man, and one not to be accounted for by 
the ordinarily presumed mode of growth of stratified epithelia ; for the deepest cells 
are greatly elongated and larger than those which are immediately superimposed, and 
have precisely the appearance of true columnar epithelium, the flat ends resting on 
the subjacent elastic lamina, and the pointed extremities directed forwards. 

The membrane of Demours or Descemet (posterior elastic lamina, Bowman), 
not very closely united with the fibrous part of the cornea, is transparent and 
glassy in appearance, firm and structureless, but very brittle and elastic ; and 

* Lectures on the parts concerned in the operations on the eye, and on the structure of 
the retina. London, 1849. 



716 



THE EYE. 



when shreds are removed they curl up always with the attached surface 
innermost. Its transparency is not impaired by acids, by boiliug in water, 
or by maceration in alkalies. In thickness it varies between 3-oVo*k an( l 
"2oVo~*k of an inch. At its circumference the membrane breaks up into 
bundles of fine threads, which are partly continued into the front of the iris, 
forming the " pillars of the iris," and partly into the fore part of the 
choroid and sclerotic coats. It is lined with an epithelial covering, which 
resembles that on serous membranes, consisting of a single layer of flat poly- 
gonal transparent cells with distinct nuclei. 

Blood-vessels and nerves. In a state of health the cornea is not provided with 
blood-vessels, except at the circumference, where they form very fine capillary loops 
and accompany the nerves. The existence of lymphatics has not been satisfactorily 
ascertained. The nerves of the cornea are very numerous, according to Schlemm.* 
Derived from the ciliary nerves they enter the fore part of the sclerotic, and are from 
twenty-four to thirty-six in number. Continued into the fibrous part of the cornea, 
they retain their dark outline for ith to ith of an inch, and then becoming trans- 
parent, ramify and form a network through the laminated structure. 



MIDDLE TUNIC OF THE EYEBALL. 

This coat consists of two parts, one a large posterior segment the choroid, 
reaching as far as the cornea, and formed chiefly of blood-vessels and pig- 
mentary material ; the other, a small anterior muscular part the irh. 
Between these and connected with both is situated the white ring of the 
ciliary muscle. 

Fig. 462. Fig. 462. CHOROID MEM- 

BRANE AND IRIS EXPOSED 

BY THE REMOVAL OP THE 
SCLEROTIC AND CORNEA 
(after Zinn). f 

a, one of the segments of 
the sclerotic thrown back ; 
&, ciliary muscle and liga- 
ment ; c, iris ; e, one of the 
ciliary nerves ; /, one of the 
vasa vorticosa or choroidal 
veins. 

THE CHOROID COAT. 

The choroid coat of 
the eye (tunica choro- 
idea s. vasculosa) is a 
dark brown membrane 
lying between the scle- 
rotic and the retina. It 
reaches forwards to the 
ciliary ligament, or 
nearly to the cornea, 

where it ends by a series of plaits or folds named ciliary processes, disposed 
in a circle projecting inwards at the back of the circumferential portion of 
the iris. Afc the hinder part, where the tunic is thickest, the optic nerve is 
transmitted through a circular opening. The outer surface is rough, and 
is connected to the sclerotic by loose connective tissue (lamina fusca of 




* Berl. Encycl. Wort. art. Augapfel, Vol. iv. p. 22. 




THE CHOROID COAT. 717 

authors), and by vessels and nerves. The inner surface, which is smooth, is 
lined by a continuous layer of pigmentary cells. 

The ciliary processes, about eighty-five in number, are arranged radiately 
in a circle. They consist of larger and smaller folds, without regular alter- 
nation, and the small folds number about one-third of the large. Each of 
the larger folds, measuring aboub -j^th of an inch in length and 4 ^th in 
depth, forms a rounded projection at its inner end, which is free from the 

Fig. 463. CILIA.RY PROCESSES AS SEEN Fig. 463. 

FROM BEHIND. f 

1, posterior surface of the iris, with the 
sphincter muscle of the pupil ; 2, anterior 
part of the choroid coat ; 3, one of the 
ciliary processes, of which about seventy are 
represented. 

pigment which invests the rest of the 
structure ; but externally they become 
gradually narrower, and disappear in 
the choroid coat : the smaller pro- 
cesses are only half as deep as the 
others. At and near their internal or 
anterior extremities the processes are 
connected by lateral loop-like projec- 
tions, and are separated from the iris by pigment. The plications of the 
ciliary processes fit into corresponding plications of the suspensory ligament 
of the lens. 

STRUCTURE. From a difference in the fineness of its constituent blood- 
vessels, the choroidal coat resolves itself into two strata, inner and outer; 
the latter containing the larger branches, and the former the capillary 
ramifications. 

In the outer part of the coat are situated the branches of the vessels. 
The arteries are large, and are directed forwards before they bend down- 
wards to end on the inner surface ; whilst the veins (vasa vorticosa) are 
disposed in curves as they converge to four of five principal trunks issuing 
from the eyeball. In the intervals between those vessels are lodged elongated 
and star-shaped pigment cells with very fine offsets, which intercommunicate 
and form a network or stroma. Towards the inner part of the tunic, this 
network passes gradually into a web without pigment : it resembles elastic 
tissue in its chemical and physical properties. 

The inner part of the choroid coat (tunica Ruyschiana s. chorio-capillaris) 
is formed by the capillaries of the choroklal vessels. From the ends of the 
large arteries the capillaries radiate in a star-like manner, and form meshes 
which are more delicate and smaller than in any other texture, and are 
finer at the back than the front of the ball. This fine network reaches as 
far forwards as about |th of an inch from the cornea, or opposite to the 
ending of the expansion of the optic nerve, where its meshes become larger, 
and join those of the ciliary processes. 

On the inner surface of the tunica Ruyschiana may be detected, according 
to various authors, a structureless transparent membrane, the membrane of 
Bruch, underlying the pigmentary layer. 

The ciliary processes have the same structure as the choroid, of which they 
are a part ; but the capillary plexus of the vessels, less fine, has meehes 



718 



THE EYE. 



with chiefly a longitudinal direction ; and tbe ramified cells, fewer in 
number, are devoid of pigment towards the free extremities of the folds. 

The pigmentary layer (choroidal epithelium, membrane of the black pig- 
ment) forms a thin dark lining to the whole inner surface of the choroid and 




Fig. 464. PIGMENT CELLS OP THE MIDDLE COAT 
(after Kolliker). 

A, small portion of the chorcid with the stellate 
or ramified cells which form its stroma. B, pigment 
cells, which cover the inner surface of the choroid ; 
a, these cells seen from the surface, of hexagonal 
form, and showing nuclei in their interior ; b, three 
of the same cells viewed edgeways ; c, molecular 
pigment, which fills the cells. 

the iris. As far forwards as the ciliary pro- 
cesses it consists of only a single layer of 
flat six-sided cells, applied edge to edge liko 
mosaic work. Each cell contains a nucleus 
and more or less dense molecular contents, 
accumulated in greatest abundance towards 
the circumference of the cell, and parrly 
obscuring the nucleus. On the ciliary pro- 
cesses and the iris the pigment is several lay- 
ers deep, and the cells, smaller and rounded, 
are so filled with dark pigment as to cover 
up the nucleus. In the eye of the albino, 

pigment is absent both from the hexagonal cells and the ramified corpuscles 

of the choroidal tunic. 

It may be mentioned that in fishes, and in many mammals, including the ox and 
the sheep, the eyes of which are often selected for dissection, the choroid, instead of 
being uniformly lined with dark pigment, presents on a greater or less extent of its 
back part a silvery layer named tapetum. The tapetum in ruminants consists of 
tendinous fibres, and in carnivora and fishes of cells, filled, in the carnivora, with 
granular matter (Leidig), in fishes with slender rods. On its inner surface is the 
tunic of Ruysch, as well as the layer of hexagonal cells, which, however, is here 
destitute of pigment. 

THE IRIS. 

The iris is the contractile and coloured membrane which is seen behind 
the transparent cornea, and gives the tint to the eye. In its centre it is 
perforated by an aperture the pupil. 

By its circumferential border, which is nearly circular, the iris is connected 
with the choroid, the cornea, and the ciliary ligament and muscles : the free 
inner edge is the boundary of the pupil, and is constantly altering its dimen- 
sions during life. The iris measures J an inch across, and, in a state of 
rest, from the circumference to the pupil about ^-th of an inch. Its surfaces 
look forwards and backwards. The anterior, variously coloured in different 
eyes, is marked by waving lines converging towards the pupil, near which 
they join in a series of irregular elevations ; and, internal to these, other 
finer lines pass to the pupil. The posterior surface is covered with dark 
pigment ; and this being removed, there is seen at the margin of the pupil a 
narrow circular band of fibres (sphincter muscle of the pupil), with which 
lines radiating inwards are blended. 



THE IRIS. 



719 



The pupil is nearly circular in form, and is placed a little to the inner 
side of the centre of the iris. It varies in size according to the contraction 
or relaxation of the muscular fibres, and this variation ranges from -g^th to 
^rd of an inch. The movements of the iris regulate the quantity of light 
admitted to the eyeball, and are associated with convergence of the optic 
axes, and with the focal adjustment of the eye. 

STRUCTURE. Fibrous and muscular tissues form the framework of the 
iris, and pigment is scattered through the texture. In front and behind is 
placed a distinct layer of pigment cells. It is still matter of discussion 
whether or not in the adult a delicate epithelium is continued from the 
margin of the cornea over the front of the iris : it is admitted to exist in 
childhood. 

The fibrous stroma consists of fibres of connective tissue directed radiat- 
ingly towards the pupil, and circularly at the circumference ; these, inter- 
weaving with one another, form a net-like web which is less open towards 
the surfaces. 

The muscular fibre is of the non-striated kind, and is disposed as a ring 
(sphincter) around the pupil, and as rays (dilatator) from the centre to the 
circumference. 



Fig. 465. 



Fig. 465. A SMALL PART OF THE 
IRIS, SHOWING THE MUSCULAR 

STRUCTURE (from Kolliker). ass 

The specimen is from the albino- 
rabbit, and has been treated with 
acetic acid : a, the sphincter muscle 
at the margin of the pupil ; 6, fas- 
ciculi of the dilatator muscle ; c, 
connective tissue with nuclear cells 
rendered clear by the acid. 



The sphincter is the flat 
narrow band on the posterior 
surface of the iris, close to 
the pupil, and w about ^th 
of &n inch wide. At the 
edge of the pupil the fibres 
are close together, but at the 
peripheral border they are 
separated, and form less com- 
plete rings. 

The dilatator, less apparent than the sphincter, begins at the ciliary or outer 
margin of the iris, and its fibres, collected into bundles, are directed inwards 
between the vessels and nerves, converging towards the pupil, and forming 
a net-work by their intercommunications. At the pupil they blend with the 
sphincter, some reaching near to its inner margin. 

Pigmentary elements. In the substance of the iris anteriorly and through- 
out its thickness are variously- shaped and ramified pigment cells like those 
in the choroid membrane. The pigment contained in them is yellow, or 
of lighter or darker shades of brown, according to the colour of the eye. On 
the fore part of the iris is a thin stratum of rather oval or rounded cells with 
granular ramified offsets (an epithelial layer Kolliker). At the posterior 
surface is a covering of dark pigment the uvea of authors ; this is con- 




720 



THE EYE. 



tinuous with the pigmentary layer lining the choroid and the ciliary pro- 
cesses, and consists of several strata of small roundish cells filled with dark 
pigment. The colour of the iris depends on the pigment ; in the different 
shades of blue eye it arises from the black pigment of the posterior surface 
appearing more or less through the texture, which is only slightly coloured 
or is colourless ; and in the black, brown, and grey eye, the colour is due 
to the pigment scattered through the iris substance. 



Fig. 466. 




Fig. 466. SECTIONAL VIEW OP THE CONNECTIONS OF THE CORNEA, SCLEROTIC, IRIS, 
CILIARY MUSCLE, CILIARY PROCESSES, HYALOID MEMBRANE AND LENS, f 

The specimen extends from the middle of the lens to the ora serrata on the inner side 
of the right eye. C, the laminated cornea; cc, conjunctiva corneae ; cs, conjunctiva 
scleroticse ; ce, epithelium of the conjunctiva ; ela, anterior elastic layer of the cornea 
passing outwards in part into the conjunctiva; elp, posterior elastic layer; U, liga- 
mentum pectinatum iridis, elastic ligament, spreading into the base of the iris, the 
sclerotic, and the attachment of the radiated ciliary muscle ; S, the sclerotic at its 
thinnest part ; A, the anterior aqueous chamber ; ap, the recess forming the posterior 
division of the aqueous chamber ; sv, placed at the junction of the cornea and sclerotic, 
points to the circular venous sinus or canal of Schlemin ; ea, epithelium behind the 
cornea indicated by a dotted line ; ei, epithelium in front of the iris similarly indicated ; 
ir, radiating muscle of the iris ; io, divided fibres of the orbicular muscle ; u, pigment 
layer or uvea ; In, centre of the crystalline lens ; Ic, capsule of the lens ; Ice, layer of 
cells in front of the lens ; cir, radiating ciliary muscle or tensor choroidese ; do, divided 
orbicular fibres ; dp, ciliary process, along the inner border of which a layer of pigment 
is continued from the choroid to the uvea, excepting at the end of the process ; Ch, 
choroid membrane ; R, the retina close to the ora serrata ; re, the ciliary part of the 
retina, the structure of which is imperfectly represented ; V, the vitreous humour ; k, 
the hyaloid membrane ; P, canal of Petit ; k', the hyaloid membrane continued behind 
the canal to the capsule of the lens ; Z, zonule of Zinn, and II, suspensory ligament of 
the lens proceeding from the hyaloid covering the ciliary process to the front of the capsule 
of the lens. 



CILIARY MUSCLE AND LIGAMENT. 721 

The vessels and nerves have a radiating arrangement through the stroma; the former 
giving rise to rings, one at the circumference, the other near the pupil ; and the latter 
forming a network. (See the description of the vessels and nerves of the vascular 
coat.) 

Pupillary membrane (membrana pupillaris). In foetal life a delicate transparent 
membrane thus named closes the pupil, and completes the curtain of the iris. The 
pupillary membrane contains minute vessels, continuous with those of the iris and of 
the capsule of the crystalline lens; they are arranged in loops, which converge towards 
each other, but do not quite meet at the centre of the pupil. At about the seventh or 
eighth month of foatal life these vessels gradually disappear; and, in proportion as the 
vascularity diminishes, the membrane itself is absorbed from near the centre towards 
the circumference. At the period of birth, often a few shreds, sometimes a larger 
portion, and occasionally the whole membrane is found persistent. (See also the 
account of the development of the eye.) 

CILIARY MUSCLE, LIG AMENTUM PECTINATUM, AND CIRCULAR SINUS. 

When the outer coat of the eyeball is separated from the choroid, a circular 
groove is seen passing round on the inner surface of the sclerotic, at its 
corneal margin. This groove is the outer wall of a venous canal, the sinus 
circularis iridis or canal of Schlemm. On the middle coat a corresponding 
groove, which completes the canal, is seen, and this is bounded in front 
by a torn membranous edge bounding the anterior surface of the iris, the 
ligameutum pectinatum, while the thickest part of the white ring of the 
ciliary muscle is behind it. This canal communicates with other venous 
spaces which give an erectile appearance to the tissue at the base of the 
ciliary processes. 

The ligamentum pectinatum consists of slight festoon-like processes of the 
fibres of the iris, lying in a transparent elastic fibrous tissue continuous with 
the posterior elastic layer of the cornea. It is a more developed structure 
in the eyes of the sheep and ox than in the human eye, and in them the 
festooned processes are prominent, giving a milled appearance like that of the 
edge of a coin. 

The ciliary muscle (Bowman) forms a ring of unstriped muscular tissue 
about T ^th of an inch broad on the fore part of the choroid. Its fibres, 
yellowish-white in colour, and longitudinal in direction, are attached in front 
to the inner surface of the sclerotic coat ; and are also connected with the 
terminal fibres of the posterior elastic layer of the cornea. From that 
origin the fibres are directed inwards and backwards in a manner which in 
a section appears radiated, and end by joining the choroid coat opposite and 
beyond the ciliary processes. The muscle is soft, and ramified pigment-cells 
are scattered through its substance. 

Concealed by the longitudinal or radiated fibres is a ring of fibres taking 
a circular direction, and which were still described as the ciliary ligament 
after the radiated fibres had been admitted to be muscular. This set consti- 
tutes the circular muscle of H. Miiller. 

The ciliary muscle appears to be in some way effective in producing the 
change in the form of the lens which takes place in accommodation of the 
eye to near vision (see Allen Thomson in " Glasgow Medical Journal" for 
1857). 

VESSELS AND NERVES OF THE MIDDLE TUNIC OF THE EYE. 

The arteries of the choroid and the ciliary processes are derived from the 
posterior and anterior ciliary vessels. The posterior consist of two sets, distin- 
guished as the short and the long. The short (posterior) ciliary branches of the 

3 B 



722 



THE EYE. 



ophthalmic artery pierce the sclerotic close to the optic nerve, and divide 
into branches which pass forward in meridional directions in the choroid 
membrane. Communicating freely they diminish in size, and entering the 
choroid form a close network of fine capillaries (tunica Euyschiana) already 
described. 



Fig. 467. 




Fig. 468. 



Fig. 467. LATERAL VIEW OP 
THE ARTERIES OF THE CHO- 
ROID AND IRIS (from Ar- 
nold), f 

a, optic nerve ; &, part of 
the sclerotic left behind, the 
greater part and the cornea 
having been removed ante- 
riorly ; c, ciliary muscle ; d, 
iris ; 1, posterior ciliary ar- 
teries piercing the sclerotic and 
passing along the choroid ; 2, 
one of the long posterior 
ciliary arteries ; 3, several of 
the short or anterior ciliary 
arteries. 

The veins of the choroid 
coat constitute an outer 
layer, partially separable 
from the arterial network, 
and easily recognised by 
the direction of the larger 
vessels. These converge 
to four nearly equidistant 
trunks, which pass through 
the sclerotic about half 
way between the margin 

Fig. 468. LATERAL VIEW OF 

THE VEINS OF THE CHOROID 

(from Arnold). 

The preparation is similar to 
that represented in the pre- 
vious figure. 1, 1, two trunks 
of the vense vorticosse at the 
place where they leave the 
choroid and pierce the sclerotic 
coat. 



of the cornea and the entrance of the optic nerve, and pour their contents 
into the ophthalmic vein. From their whorl-like arrangement they are 
known as the vasa vorticosa. 

The blood-vessels of the ciliary processes are very numerous, and are derived 
from the anterior ciliary, and from those of the fore part of the choroidal 
membrane. Several small arterial branches enter the outer part of each ciliary 
process, at first running parallel to each other and communicating sparingly. 
As they enter the prominent folded portion, the vessels become tortuous, sub- 
divide minutely, and inosculate frequently by cross branches. Finally they 
form short arches or loops, and turn backwards to pour their contents into 
the radicles of the veins. 

On the free border of the fold, one artery, larger than the rest, extends 




BLOOD-VESSELS OF THE IRIS. 723 

the whole length of each ciliary process, and communicates through inter- 
veuing vessels with a long venous trunk which runs a similar course on the 
attached surface. 

Fig. 469. 




Fig. 469. INJECTED BLOOD-VESSELS OF THE CHOROID COAT (from Sappey). & 

1, one of the larger veins ; 2, small communicating vessels ; 3, branches dividing into 
the smallest vorticose vessels. 

Arteries of the iris. The special arteries of the iris are the long ciliary 
and the anterior ciliary. 

The long (posterior) ciliary arteries, two in number, and derived from the ophthal- 
mic, pierce the sclerotic a little before, and one on each side of, the optic nerve. 
Having gained the interval between the sclerotic and choroid coats, they extend 
horizontally forwards through the loose connective tissue (membrana fusca) to the 
ciliary muscle. In this course they lie nearly in the horizontal plane of the axis of the 
eye-ball, the outer vessel being however a little above, and the inner one a little below 
the level of that line. A short space behind the fixed margin of the iris each vessel 
divides into an upper and a lower branch, and these, anastomosing with the corre- 
sponding vessels on the opposite side and with the anterior ciliary, form a vascular 
ring (circulus major) in the ciliary muscle. From this circle smaller branches arise 
to supply the muscle; whilst others converge towards the pupil, and there, freely com- 
municating by transverse offsets from one to another, form a second circle of anasto- 
mosis (circulus minor], and end in small veins. 

The anterior ciliary arteries, five or six in number, but smaller than the vessels 
just described, are supplied from the muscular and lachrymal branches of the ophthal- 
mic artery, and pierce the sclerotic about a line behind the margin of the cornea ; 
finally, they divide into branches which supply the ciliary processes, and join the 
circulus major. 

Besides these special arteries, numerous minute vessels enter the iris from the ciliary 
processes. 

The veins of the iris follow closely the arrangement of the arteries just 
described. The circular sinus communicates with this system of vessels. 

3 B 2 



724 



THE EYE. 



The nerves for the supply of the iris are named ciliary : they are nume- 
rous and large ; and, before entering the iris, divide in the substance of the 
ciliary muscle. 



Fig. 470. 



Fig. 471. 





Fig. 470. VESSELS OP THE CHOROID, CILIARY PROCESSES AND IRIS OF A CHILD (from 
Kolliker after Arnold). >-<> 

a, capillary network of the posterior segment of the choroid ending at , the ora 
serrata ; c, arteries of the corona ciliaris, supplying the ciliary processes d, and passing 
into the iris e ; f, the capillary network close to the pupillary margin of the iris. 

Fig. 471. FRONT VIEW OF THE BLOODVESSELS OF THE CHOROID COAT AND IRIS FROM 
BEFORE (from Arnold). !_ 

A, interior part of the choroid : B, iris ; C, ciliary muscle, &c. ; 1, 1, long posterior 
ciliary arteries ; 2, five of the anterior ciliary arteries ramifying towards the outer margin 
of the iris ; 3, loop of communication between one of the anterior and one of the long 
posterior ciliary arteries ; 4, internal circle and network of the vessels of the iris ; 5, 
external radial network of vessels. 



Fig. 472. Fig. 472. LATERAL VIEW OF THE CILIARY 

NERVES (from Arnold). 

a, optic nerve ; b, hack part of the sclerotic ; 
c, ciliary muscle, &c. ; d, iris ; e, outer surface 
of the choroid coat; 1, five of the ciliary nerves 
passing along the sheath of the optic nerve, 
piercing the sclerotic posteriorly, and thence 
passing forward on the choroid membrane to 
the ciliary muscle and iris. The nerves are 
represented too large. 

The ciliary nerves, about fifteen in num- 
ber, and derived from the lenticular ganglion 

and the nasal branch of the ophthalmic division of the fifth nerve, pierce the 
sclerotic near the entrance of the optic nerve, and come immediately into contact with 




RETINA OR XERYOUS TUXIC. 725 

the choroid. They are somewhat flattened in form, are partly embedded in grooves 
on the inner surface of the sclerotic, and communicate occasionally with each other 
before supplying the cornea and entering the ciliary muscle. AY hen the sclerotic is 



Fig. 473. 




Fig. 473. DISTRIBUTION OP 
NERVES IN THE IRIS (from 
Kolliker). 5JL 

The preparation was taken from 
the eye of an albino rabbit, and 
Avas treated with soda, a, smaller 
branches of the ciliary nerves ad- 
vancing from the choroid ; 6, loops 
of union between them at the mar- 
gin of the iris ; c, arches of union 
in the iris ; </, finer network in the 
inner part; d, some of the termi- 
nations of single nerve- filaments 
in the outer part of the iris ; e, 
sphincter pupillae muscle. 



carefully stripped from the subjacent structures, these nerves are seen lying on the 
surface of the choroid. Within the ciliary muscle the nerves subdivide minutely, a few 
being lost in its substance, but the greater number pass on to the iris. In the iris the 
nerves follow the course of the blood-vessels, dividing into branches, which com- 
municate with one another as far as the pupil. In the iris they soon lose their dark 
outline, and their mode of termination is not ascertained. 

RETINA OR NERVOUS TUNIC. 

The retina is a delicate almost pulpy membrane, which contains the ter- 
minal part of the optic nerve. It lies within the choroid coat, and rests on 
the hyaloid membrane of the vitreous humour. It extends forwards nearly 
to the outer edge of the ciliary processes of the choroid, where it ends in a 
finely indented border or a serrata. From this border there is continued 



Fig. 474. THE POSTERIOR HALF OF THE Fig. 474. 

RETINA OP THE LEFT ETE VIEWED 
FROM BEFORE (after Henle). f 

s, the cut edge of the sclerotic coat ; 
ch, the choroid ; ?*, the retina : in the 
interior at the middle the macula lutea 
with the depression of the fovea centralis 
is represented by a slight oval shade ; 
towards the left side the light spot 
indicates the colliculus or eminence at 
the entrance of the optic nerve, from the 
centre of which the arteria centralis is 
seen spreading its branches into the 
retina, leaving the part occupied by the 
macula comparatively free. 

onwards a thin layer of transparent 

nucleated cells (not nerve-elements) 

of an elongated or cylindrical form, 

constituting the pars ciliaris retinae. 

which reaches as far as the tips of the ciliary processes, and there gradually 

disappears. The thickness of the retina diminishes from behind forwards. In 

the fresh eye it is translucent and of a light pink colour ; but after death it 

soon becomes opaque, and this change is most marked under the action of 




726 THE EYE. 

water, alcohol, and other fluids. The outer surface is rough or slightly 
flocculent when the choroid is detached, and is in contact with the pig- 
mentary layer ; and from it a more or less complete stratum may be raised 
with care in a perfectly fresh eye. This layer, at first called membrane of 
Jacob from its discoverer, is now generally recognised as the columnar layer. 
The inner surface of the retina is smooth, and is merely applied to the 
vitreous body within it : on it the following objects may be seen. In the 
axis of the ball is a yellow spot macula lutea (limbus luteus, Sommerriug), 
which is somewhat elliptical in shape, and about -^th of an inch in diameter : 
in its centre is a slight hollow, fovea centralis, and, as the retina is thinner 

Fig. 475. 




Fig. 475. SECTION THROUGH THE MIDDLE OP THE OPTIC NERVE AND THE TUNICS OP THE 
EYE AT THE PLACE OP ITS PASSAGE THROUGH THEM (from Kolliker after Ecker). f 

The drawing was taken from a chromic acid preparation : a, arteria centralis retinae ; 
6, fasciculi of optic nerve fibres with neurilemuia ; c, sheath of the optic nerve, passing 
into </, the sclerotic coat ; c", outermost pigmental layer of the choroid or membraua 
fusca ; d, choroid and inner pigment-layer ; e, /, columnar layer of the retina ; g, the 
two granular layers ; A, layer of nerve-cells ; i, layer of nerve-fibres ; &, colliculus or 
eminence at the entrance of the optic nerve ; I, lamina cribrosa. 

here than elsewhere, the pigmentary layer of the choroid is visible through 
it, giving rise to the appearance of a hole through the tunic. About T ^th of 
an inch inside the yellow spot is the round disc, porus opticus, where the 
optic nerve expands, and in its centre the point from which the vessels of 
the retina branch. At this place the nervous substance is slightly elevated 
so as to form an eminence (colliculus nervi optici). 

STRUCTURE. The retina, when examined microscopically in vertical 
sections, exhibits a series of dissimilar strata, together with structures not 
confined to one stratum. (1st) Externally is the columnar layer ; (2nd), 
in the middle is the granular layer, comprising the external nuclear, the 
iuternuclear, the internal nuclear, aud the molecular layers ; and (3rd) 
internally is the nervous layer, consisting of three strata, one of nerve-cells, 
another of nerve-fibres the ramifications of the optic nerve, and, on the 
inner surface of this last, a limiting membrane. (4th) Traversing the strata 
from the columnar layer to the limiting membrane, are placed vertical fibrils 
of varying kinds at different depths, and not fully ascertained to be con- 
tinuous, the radiating fibres of Miiller. (5th) Blood-vessels distributed 
in the retina, are placed chiefly towards the inner surface. 



COLUMNAR LAYER OF THE RETIXA. 



727 



1. The columnar layer (stratum bacillorum), consists of innumerable thin 
rods, placed vertically side by side like palisades, and of other larger bodies, 
more or less thickly interspersed amoog these, and named cones. These 



Fig. 476. 



Fig. 476. VERTICAL SECTION OP A SMALL PART OF 
THE RETINA (after Kolliker). ^ 

A, entire section of a small part of the retina ; B, 
two cones represented separately in their connection 
with the fibres of Miiller and other structures ; C, 
two rods represented separately iu their connection 
with the granules, fibres of Miiller, and the nerve- 
cells ; 1, columnar layer ; a, in A and C, the rods, 
in B, the terminal part of the cone ; b, cones ; 2, 
granular layer ; c, outer layer of nuclei (striated 
corpuscles of Henle) ; d, inner layer of nuclei ; /, 
internuclear layer ; 3, nervous layer ; g, fiue mole- 
cular substance outside h, the nerve-cells ; &, nerve- 
fibres ; I, membraua liinitans ; e, inner ends of the 
fibres of Miiller resting on the limiting membrane. 



structures are glistening, soft, easily des- 
troyed, and lose their characters quickly in 
fluids. The rods are of uniform diameter, 
and are abruptly truncated externally. The 
cones are flask-shaped in the inner part of their 
extent, and taper to a rod-like extremity ex- 
ternally. Each cone rests on a pyriform cell 
continuous with it, and forming the extremity 
of a fibre of Miiller ; while the rods end 
internally in pointed extremities ranging with 

these pyriform cells, and represented as formed by similar bodies (Kolliker); 
but this continuity with Miillerian fibres is still disputed. The dilated 
portions of the cones present granular contents, and a similar appearance is 
described in the inner halves of the rods. At the outer ends the rods pro- 
ject somewhat farther than the cones. When the outer surface of the 
retina is viewed about midway between its centre and margin with a strong 
enough magnifying power, a number of minute globular-looking bodies, the 
ends of the rods, appear ; and between them, at a deeper level, other 




Fig. 477. 



Fig. 477. OUTER SURFACE OP THE COLUMNAR LAYER OP 
TBE RETINA (from Kolliker). - 

a, part of the columnar layer within the macula lutea, 
where only cones are present ; b, part near the macula, 
where a single row of rods intervenes between the cones ; c, 
from a part of the retina midway between the macula and 
the ora serrata, showing a preponderance of the rods. 



transparent larger bodies, the swellings of the cones, 
are seen, with a smaller circle within each the end 
of its narrower part. Towards the margin the rods 
become more numerous ; near the centre the cones 
predominate ; and in the macula lutea the cones alone are seen. 

2. The external and internal nuclear divisions of the granular layer are 
two collections of rounded and oval corpuscles, refracting light pretty strongly. 
The corpuscles of the internal nuclear layer are small cells with large nuclei, 




728 THE EYE. 

as are also some, at least, of those of the outer layer, namely, the pyriform 
bodies supporting the cones. But, according to recent investigations of 
Henle, whose statements have been corroborated by Ritter as holding good 
in the mammals generally, the bodies which constitute the bulk of the outer 
nuclear layer, are elliptical corpuscles, which, when perfectly fresh, exhibit 
transverse striation similar to muscular fibre, to the extent of three dark 
lines alternating with clear substance in each, but which soon break up into 
globules. 

Fig. 478. Fig. 478. STRIPED ELLIPTICAL CORPUSCLES OP THE EXTERNAL NUCLEAR 
LAYER OF THE RETINA (from Henle). ^-p 

The internuclear layer, which lies between the layers now 
referred to, is a clear space of unequal depth, vertically striated, 
and having likewise a molecular appearance. The molecular 
basis is more marked in a thin stratum which intervenes be- 
tween the internal nuclear layer and the nerve-cells, and which, 
therefore, has been distinguished as the molecular layer. 

3. Nervous layer. a. The cellular layer consists of nerve-cells with a 
fine molecular material interspersed among them. At the bottom of the 
eye over the yellow spot they are thickest (from 8 to 10 cells deep), and 
decrease in quantity in front ; so that at a fifth of an inch from the ora 
serrata they are only scattered in clusters. Around the entrance of the 
optic nerve there is only a single stratum of these elements. The cells whon 
fresh are transparent and nucleated, being roundish or pear-shaped in out- 
line, and are furnished with from two to six ramified offsets. By their 
internal offsets the cells are continuous with the nerve-fibres beneath ; by 
horizontal offsets they are united one with another ; and by those which 
pass outwards they are connected with the corpuscles of the internal nuclear 
layer. 

6. The nerve-fibre layer consists of nerve-fibres directed forwards from the 
optic nerve, and collected into small bundles, which, compressed laterally, 
intercommunicate and form a delicate web with narrow elongated meshes. 
This stratum diminishes in thickness forwards, and ends at the ora serrata : 
it forms a continuous membrane, except at the yellow spot, where the nerve 
fibres are wanting. According to Bowman, the fibres, which lose their dark 
outline on reaching the retina, consist there of an axis-cylinder only. It is 
now well established that they terminate in the nerve-cells on which they 
lie, and this is the only mode of their termination which has been fully 
ascertained. 

c. Membrana limitans and connective tissue. The limiting membrane lines 
the inner surface of the retina, separating it from the vitreous body. It is 
an extremely thin and delicate membrane, which can be detached in shreds; 
and it agrees with the other glassy membranes of the eye-ball in not being 
affected by alkalies, maceration, or boiling. On its retinal surface it is 
studded with the broadened insertions of vertical threads of connective tissue, 
which separate the nerve-fibres into bundles, ar,d form the inner parts of the 
Miillerian fibres. Nuclei apparently exist both in these and in the mem- 
brana limitaus itself. Delicate homogeneous connective tissue, likewise, 
enters into the composition of the layers of the retina as far outwards as the 
bases of the rods and cones, and gives there the appearance of a horizontal 
line, the external limitary membrane of Schultze. 

4. Radiating fibre s of Multer, and connections of the different elements of the 
retina. From the foregoing description it will be gathered that the history of 



MULLEKIAN FIBRES. BLOOD-VESSELS OF EETINA. 729 

the Mtillerian fibres is still incomplete. Indeed, the minuteness and delicacy 
of their structure renders their investigation one of the most difficult sub- 
jects of anatomical inquiry. Heinrich Miiller, to whom science chiefly owes 
the advance which has of late years been made towards the elucidation of 
the minute structure of the retina, described radiating fibres, extending verti- 
cally from the rods and cones to the membrana limitans, interrupted in their 
course by the corpuscles of the outer and inner nuclear layers, and connected 
with the nerve-cells. He subsequently recognised the vertical fibres in the 
internal layers as connective tissue, a view now universally adopted. It 
appears to be clearly established, that from the pyriform corpuscles at the base 
of each cone a thread passes inwards to a corpuscle of the internal nuclear 
layer. It is also stated that more slender threads unite the rods with the 
deep layers ; and Kolliker represents a thread passing out from a corpuscle 
of the internal nuclear layer as afterwards dividing into branches, on which 
are placed corpuscles of the external nuclear layer, and which terminate in 
rods. This account of the structure seems best to accord with the physio- 
logical view now very generally held, that the columnar layer is the more 
immediate seat of the formation of a distinct image in vision, and of the 
reception of visual impressions from rays of light impinging upon the retina. 
It is right to state, however, that a different view is taken by Henle, who 
believes that the rods are free, and that the fibres observed by H. Miiller 
and Kolliker are artificial products, the result of coagulation by re-agents. 
Heule regards the retina as composed of an outer part, which he terms the 
mosaic layer, and which comprises the columnar structures of Jacob's mem- 
brane, and the external nuclear layer, and is destitute of blood-vessels ; and 
an inner nervous part comparable to the structure found in the cerebral con- 
volutions, and consisting of a stratum of nerve fibres and of two strata of 
nerve cells alternating with granular strata ; the corpuscles of the internal 
nuclear layer being considered by him as nerve cells of a smaller order than 
those of the cellular layer. 

5. Vessels of the retina. An artery enters and a vein leaves the retina 
between the bundles of fibres of the optic nerve. 

The artery (arteria centralis retinae) is an offset of the ophthalmic, and 
divides into four or five primary branches as soon as it enters the eye-ball. 
These larger offsets are situated at first on the inner surface of the nerve 
fibres, but they soon pass between these into the stratum of nerve-cells, 
where they form a network of very fine capillaries with rather wide meshes, 
which reaches in front to the ora serrata. 

The vein corresponding to this artery has a similar distribution : it termi- 
nates in the ophthalmic vein. In animals there is a circular vessel (circulus 
venosus retina) following the line of the ora serrata. 

Constituents of the retina in the yellow spot. In this part of the retina 
the several layers above described undergo some modification : the following 
are the alterations in the strata from without inwards. In the columnar 
layer, only the cones are present, but they are set close together, and are 
smaller than elsewhere. The granular layer is absent opposite the fovea 
ceutralis. The nervous layer is thus modified : the nerve-cells cover the 
whole spot, like laminated epithelium, and rest internally on the membrana 
limitans ; but the molecular substance outside them is absent over the 
fovea centralis ; the nerve-fibres extend only into the circumference of the 
spot amongst the cells, without forming a layer over it. The fibres of 
Miiller are found at the circumference but not over the fovea centralis ; they 
have an oblique, almost horizontal direction, and present a specially nerve- 



730 THE EYE. 

like appearance. Only capillary vessels occupy the yellow spot, the larger 
branches passing round it. 



Fig. 479. 




Fig. 479. VERTICAL SECTION OP THE RETINA THROUGH THE MIDDLE OP THE FOVEA 
CENTRALIS (from Henle.) ~- 

This figure is taken from a preparation of the human retina hardened in alcohol, and 
is designed to show the peculiarities of this part as compared with other regions of the 
retina, viz., the obliquity of the Miillerian fibres, the thinness of the layer of nerve- 
fibres, and the absence of the granular layer in the centre, a, 6, cones of the columnar 
layer ; c, external nuclear layer ; d, internal nuclear layer ; /, external fibrous layer ; 
g, molecular substance next to h, the ganglionic layer ; Tc, the layer of nerve-fibres ; 
I, the internal limiting membrane. 



The yellow colour of the macula lutea is deepest towards the centre, and 
is due to a pigment which imbues all the layers except the columnar : it 
does not appear to be contained in cells, and is soon removed after death by 
the action of water. 

Ciliary part of the retina. The structure which has been named the 
ciliary part of the retina is situated in front of the ora serrata, and extends 
thence over the inner ends of the ciliary processes to the base of the iris 
(therefore, over the whole corona ciliaris). Though entirely destitute of the 
nervous parts of the retinal structure, it is still in continuity with the sub- 
stance of the retina, and in the form of a grey membrane, adheres to the 
ciliary processes and zonule of Zinn, and is usually in great part detached 
from the neighbouring parts along with the latter. According to Kolliker, 
this layer consists of elongated nucleated cells, which in the human subject 
are broad externally, and with flat or forked bases set upon the internal 
limiting membrane. He regards these cells as probably corresponding to the 
Miillerian fibres, and as constituting in this place the only representative of 
the retinal structure. 



THE VITREOUS BODY. 



731 



On the structure of the retina may be consulted Heinrich Miiller, in Siebold und 
Kolliker's Zeitschrift, 1851 and 1856; M. Schultze, "Obs. de retinae Struct, penit.," 
1859 ; Goodsir, in Edin. Med. Journal, 1855 ; Kolliker, Handbuch d. Gewebelehre, 
4th ed., 18(53 ; and Henle, Handbuch d. System. Anatomic, vol. ii., 1866. 



Fig. 480. 



Fig. 481. 






Fig. 480. VERTICAL SECTION THROUGH THE CJIOROID AND RETINA KEAR THE ORA 
SERRATA (from Kolliker). f 

a, hyaloid membrane ; of, indications of fibres which radiate from the anterior margin 
of the retina into the vitreous body ; 6, limiting membrane and fibrous layer of the 
retina ; c, ganglion! c layer with a few cells shown ; d, inner nuclear layer ; e t inter- 
nuclear substance ; /, outer nuclear layer ; g, columnar layer ; h, dark pigment ; i, 
middle layer of the choroid ; I, beginning of one of the ciliary processes ; m, ciliary part 
of the retina. (The recess shown at a' is not constant.) 

Fig. 481. A SMALL PORTION OF THE CILIARY PART OF THE RETINA (from Kolliker). ^~ 2 - 
A, human ; B, from the ox j 1, pigment-cells ; 2, cells forming the ciliary part. 



THE VITKEOUS BODY. 

The vitreous body is the largest of the transparent parts occupying the 
centre of the eye-ball. Globular in form, it occupies about four- fifths of the 
ball, and supports the delicate retina, being in contact with the membrana 
limitans. On the fore part it is hollowed out for the reception of the lens 
and its capsule, and behind it is more closely connected with the retina than 
at the sides, having received at that part offsets of the retinal vessels in 
foetal life. It is quite transparent, and like a thin jelly in its interior. Its 
surface is formed by a thin enveloping glassy membrane, named hyaloid, and 
as long as this membrane is entire, it retains its form in water. No vessels 
enter it, and its nutrition must be therefore dependent upon the surrounding 
vascular textures viz., the retina, and the ciliary processes. 

The hyaloid is an extremely thin and clear membrane. When traced 
forwards it is found to be connected, opposite the outer part of the ciliary 
processes, with a firm membrane passing in front of the marginal part of 
the lens (suspensory ligament), while a thinner layer, proceeding inwards 
from this, becomes united with the posterior layer of the capsule of the 
lens, so that it is doubtful whether or not the membrane is prolonged 
between the capsule and the vitreous body. On the inner surface of the 
hyaloid are a few delicate nuclei. Fibres have been supposed to be pro- 



732 



THE EYE. 



longed inwards from it, to form cells for the contained fluid, but obser- 
vations with the microscope do not show any in the adult, though in the 
foetus there are fibres in the interior of the vitreous mass, with "minute 



Fig. 482. 




Ic 



Fig. 482. VERTICAL SECTION OF A PART OP THE EYEBALL, SHOWING THE CONNECTIONS OP 
THE CORNEA, SCLEROTIC, IRIS, CILIARY MUSCLE, HYALOID, AND LENS, f 

The full description of this figure will be found at p. 720 ; the following references 
apply to the lens and parts connected with it. A, the anterior aqueous chamber in front 
of the pupil ; ap, the recess forming the posterior division of the aqueous chamber, the 
iris resting between this and the pupil on the surface of the lens ; ir, radiating fibres of 
the iris or dilatator pupillse muscle ; to, orbicular fibres or sphincter muscle ; u, pigment 
layer of the iris or uvea ; In, the lens at its centre ; Ic, its capsule ; Ice, granular or 
cellular layer in front of the lens ; this layer is seen to terminate abruptly at the margin 
of the lens, where the new fibres of the lens are developed, and from whence the nuclei 
of the fibres extend for a certain depth inwards in an irregular plane in the growing 
lens ; A, the hyaloid membrane ; Z, the zonule of Zinn ; P, the canal of Petit ; II, 
in front of it the suspensory ligament of the lens ; h', the part of the hyaloid which 
closes the canal of Petit behind and extends to the posterior surface of the lens ; V, the 
vitreous humour. 



nuclear granules" at their point of junction. (Bowman.) It is still 
doubtful how far the appearances of lamination produced by the action of 
chromic acid, or of radiated fibrillation resulting from congelation, are true 
indications of any actually existing structure in the interior of the vitreous 
humour. 

The fluid collected from the vitreous body by puncturing it resembles 
water : it contains, however, some salts with a little albumen. 



THE LEXS. 733 



THE LENS AND ITS CAPSULE. 

The lens, enclosed in a capsule, is situated behind the pupil, and in front 
of the vitreous body. 

The capsule of the lens, a transparent glass-like membrane closely sur- 
rounding the contained body, is hard and brittle, especially in front, but 
very elastic and permeable to fluid. The anterior surface is in contact with 
the iris towards the pupil, and recedes from it slightly at the circumference ; 
the posterior rests closely on the vitreous body. Around the circumference 
is a space to be afterwards noticed, the canal of Petit. The fore part of the 
capsule is several times thicker than the back, as far out as to -y^-th of an 
inch from the circumference, where the suspensory ligament joins it ; but 
beyond that spot it becomes thinner, and it is thinnest behind. Tn its nature 
the capsule of the lens resembles the glassy membrane at the back of the 
cornea, for it is structureless, and remains transparent under the action of 
acids, alcohol, and boiling water ; and when ruptured, the edges roll up 
with the outer surface innermost. (Bowman.) 

Connecting the anterior wall of the capsule closely to the lens is a single layer of 
granular and nucleated polygonal cells, which ends abruptly where the capsule comes 
in contact with the hyaloid membrane. The place of termination of this cellular 
layer round the margin of the lens corresponds to the line from which the fibres of 
the lens are developed. There is no such layer of cells on the posterior wall of the 
capsule, but in hardened specimens various reticulated appearances may be detected, 
which probably arise, as supposed by Henle, from the pressure one on another of glo- 
bules of a fluid separated from the lens after death, and known as liquor Morgagni. 

No vessels enter the capsule of the lens in the adult. In the foetus it receives an 
artery behind, which is named the capsular artery. This vessel leaves the arteria 
centralis retinae at the centre of the optic nerve, and passing through the substance of 
the corpus vitreum, enters the posterior portion of the capsule of the lens, where it 
divides into radiating branches. These form a fine network, turn round the margin of 
the lens, and extend forwards to become continuous with the vessels in the pupillary 
membrane and the iris. 

Some authors (Albinus, Zinn, &c.) state that they have traced vessels from the 
capsule into the substance of the lens itself. 

THE LENS. 

The lens (lens crystalliua) is a doubly convex transparent solid body, with 
a rounded circumference. Its convexity is not alike on the two surfaces, 

Fig. 483. LAMINATED STRUCTURE OF THE CRYSTAL- Fig. 483. 

LINE LENS (from Arnold). * 

The laminae are split up after hardening in alcohol. 
1, the denser central part or nucleus; 2, the succes- 
sive external layers. 

being greatest behind, and the curvature is 
less at the centre than towards the margin. 
It measures about ^rd of an inch across, and 
^-th from before backwards. In a fresh lens 
the outer portion is soft and easily detached ; 
the succeeding layers are of a firmer consis- 
tence ; and in the centre the substance becomes 

much harder, constituting the nucleus. On the anterior and posterior 
surfaces are faint white lines directed from the poles towards the cir- 
cumference ; these in the adult are somewhat variable and numerous on 




734 



THE EYE. 



the surface, but in the foetal lens throughout, and towards the centre of the 
lens in the adult, they are three in number, diverging from each other like rays 
at equal angles of 120. The lines at opposite poles have an intermediate 
position (not being over one another) : they are the edges of planes or septa 
projecting vertically inwards to the centre of the lens, and receiving the ends 
of the lens-fibres which are collected upon them. 




Fig. 484. OUTLINES ILLUSTRATING THE COURSE OP THE FIBRES IN THE POSTAL 
CRYSTALLINE LENS. | 

This diagram represents the typical or more simple state of the fibres in the full- 
grown foetal or infantile condition ; the three dotted lines radiating at equal angles of 
120 from the centre indicate the position of the intersecting planes, where they reach 
the surface; the figures 1, 2, 3, 4, 5, and 6, indicate certain fibres selected arbitrarily at 
equal distances in one- sixth part of the lens to show their course from the front to the 
back ; A, the anterior surface ; B, the posterior surface ; C, the lateral aspect : in these 
several figures, for the sake of clearness, a few lines only are introduced into the upper 
third, while in the lower two-thirds a greater number are marked ; but no attempt is 
made to represent the number existing in nature ; the parts of the dotted line marked c, 
are on a level with the centre of the several lenses. 



p. 4 gg Fig. 485. FRONT VIEW OF THE FIBROUS 

STRUCTURE OP THE ADULT LENS (from 
Sappey after Arnold), f 

In this figure more numerous planes of 
intersection of the fibres are shown than 
in fig. 484. 

STKUCTUKE. When the lens has 
been dried, or hardened by immer- 
sion in spirit, boiling water, or other 
fluid capable of rendering it firm 
and white, concentric laminae, nar- 
rowing to a point at the poles, may 
be detached from it. The laminae 
are further composed of microscopic 
fibres, which adhere together by 
wavy or slightly serrated margins. 

The lens is albuminous in its composition, and is devoid of blood-vessels ; 

and at the planes of intersection a finely granular homogeneous material 

takes the place of the fibres. 




FIBRES OF THE LENS. 



735 



The fibres of the lens are somewhat flattened threads, about 3-^^th of an 
inch wide, and are directed over the edge of the lens from the planes on one 
surface to those on the other. In their course between the opposite surfaces, 
no fibre passes from pole to pole, but the fibres beginning in the pole or 
centre of one surface terminate in the end of a plane on the opposite sur- 
face, and vice versa ; the intervening fibres passing to their corresponding 
places between. Some of the superficial fibres possess transparent nuclei, at 
nearly regular intervals. In the more superficial fibres of the growing lens 
the nuclei occupy very regularly the equatorial part. At their ends, 
where the fibres meet the planes, they are soft and indistinct ; and at the 



Fig. 486. MAGNIFIED VIEW OF THE FIBRES 
OF THE CRYSTALLINE LENS. 

A, longitudinal view of the fibres of the 
lens from the ox, showing the serrated edges. 
B, transverse section of the fibres of the lens 
from the human eye (from Kolliker). C, 
longitudinal view of a few of the fibres from 
the equatorial region of the human lens 
(from Henle). ^ The most of the fibres 
are seen edgeways, and, towards 1, present the 
swellings and nuclei of the "nuclear zone ;" 
at 2, the flattened sides of two fibres are 



middle part, where they are placed 
on the margin of the lens, they are 
widest and best marked. The fibres 
are six-sided prisms, flattened in the 
plane of the lamina in which they lie. 
The edges are bevelled and sinuous ; 
they are very regularly toothed at the 
edges in fishes and some other animals 

Fig. 487. 



Fig. 486. 




Fig. 487. CELLS CONNECTING THE LENS WITH 
ITS CAPSULE (from Bowman). 




for more perfect junction with those in the same plane ; but in man and 
mammals, the edge is only slightly jagged or irregularly serrated. 

Changes in the lens by age. In the foetus, the lens is nearly spherical : it 
has a slightly reddish colour, is not perfectly transparent, and is softer, and 
more readily broken down than at a more advanced age. 



736 THE EYE. 

In the adult, the anterior surface of the lens becomes more obviously less 
convex than the posterior ; and the substance of the lens is firmer, colour- 
less, and transparent. 






o 



Fig. 488. Fig. 488. SIDE VIEWS OF THE LENS AT DIFFERENT AGES. 

h C a, at birth with the deepest convexity ; 6, in adult life 

with medium convexity ; c, in old age with considerable 
flattening of the curvatures. 



In old age, it is more flattened on both sur- 
faces ; it assumes a yellowish or amber tinge, and 
is apt to lose its transparency as it gradually increases in toughness and 
specific gravity. 



SUSPENSORY LIGAMENT OF THE LENS AND CANAL OF PETIT. 

The suspensory ligament of the lens Retzius (Zonula of Zinn) is a 
slender but tolerably firm transparent membrane, which, attached to the 
fore part of the capsule of the lens close to its circumference, passes out- 
wards to join the hyaloid membrane of the vitreous humour at its most 
anterior convex part, opposite the ora serrata of the retina, and assists in 
retaining the lens in its place. On the anterior surface small streaks of 
pigment are observable after its separation from the other membranes, and 
when this pigment is removed by washing, small but regular folds processus 
ciliares zonulse come into view near the lens ; these are plaits in the 
membrane, and are received into the intervals between the ciliary processes 
of the choroid coat, into which they fit. Between the folds and the lens- 
capsule is a slight interval free from plaits, which forms part of the boundary 
of the posterior aqueous chamber. The posterior surface is turned towards 
the hyaloid membrane, from which it is separated near the lens by a space 
named the canal of Petit. 

The suspensory ligament has chemical properties similar to those of the 
capsule of the lens, but in it parallel or slightly radiating longitudinal fibres 
may be recognised, which are stiff, elastic, and pale, resembling those of 
elastic tissue, being less pliable, and less acted on by acetic acid than those 
of connective tissue. 



Fig. 489. Fig. 489. VIEW FROM BEFORE OF THE CANAL OF PETIT 

INFLATED (from Sappey). 

The anterior parts of the sclerotic, choroid, iris and cornea 
having been removed, the remaining parts are viewed from 
before, and the canal of Petit has been inflated with air 
through an artificial opening. 1, front of the lens ; 2, 
vitreous body ; 3, outer border of the canal of Petit ; 4, outer 
part of the zonule of Zinn ; 5, appearance of sacculated 
dilatations of the canal of Petit. 

The canal of Petit is the interval surrounding 

the edge of the lens-capsule, bounded in front by the suspensory liga- 
ment, and behind by the hyaloid membrane. Its width is about ^th of 
an inch. On blowing air into it through an opening in the anterior 
boundary, the plaits of the suspensory ligament on its front are distended, 
and the canal presents a sacculated appearance. 




DEVELOPMENT OF THE EYE. 



737 



AQUEOUS HUMOUR AND ITS CHAMBER. 

The aqueous humour fills the space in the fore part of the eyeball, be- 
tween the cornea and the capsule of the lens with its suspensory ligament. 
The iris, resting in part upon the lens, divides the aqueous chamber partially 
into two. The aqueous humour differs little from water in its physical cha- 
racters ; but it contains a small quantity of some solid matter, chiefly chlo- 
ride of sodium, dissolved in it. 

The chambers, into which the space containing the aqueous humour is di- 
vided by the iris, are named respectively the anterior and posterior. This 
subdivision is incomplete in the adult, but in the foetus before the seventh 
month it is completed by means of the inembrana pupillaris, which by its 
union with the margin of the pupil closes the aperture of communication be- 
tween the two chambers. 

The anterior chamber is limited in front by the cornea and behind by the 
iris, while opposite the pupil it is bounded by the capsule of the lens. 

The posterior chamber was originally so named in the belief that a free 
space intervened between the iris and the capsule of the lens. It is now, 
however, well ascertained by observations on the living eye, and by sections 
made in the frozen state, that the pupillary margin and part of the posterior 
surface of the iris are in contact with the capsule of the lens ; and the term 
posterior chamber can therefore be employed only to indicate the want of 
continuity between those opposed structures, where no space actually inter- 
venes, and to the angular interval existing at the circumference between the 
ciliary processes, the iris, and the suspensory ligament. 

DEVELOPMENT OF THE EYE. 

The eyes begin to be developed at a very early period, in the form of two hollow 
processes projecting one from each side of the first primary cerebral vesicle. Each 
process becomes converted into a flask-shaped vesicle, called the primary optic vesicle, 
which communicates by a hollow pedicle with the base of the posterior division of the 
first primary cerebral vesicle. (See p. 578, and fig. 386 B.) According to the obser- 
vations of Remak on the chick, the pedicles, originally separate, come together, and 
their cavities temporarily communicate, a condition which may explain the forma- 
tion of the optic commissure. The primary optic vesicle comes into contact at its 
extremity with the cuticle, which somewhat later becomes invaginated at this point, 
and forms a small pouch pressing inwards on the optic vesicle ; the aperture of this 

Fig. 490. LONGITUDINAL SECTION 
OP THE PRIMARY OPTIC VESICLE 
IN THE CHICK MAGNIFIED (from 
Remak). 

A, from an embryo of sixty-five 
hours ; B, a few hours later ; C, 
of the fourth day ; c, the corneous 
layer or epidermis, presenting in 
A, the open depression for the 
lens, which is closed in B and C ; 
I, the lens-follicle and lens; pr, 
the primary optic vesicle ; in A 
and B, the pedicle is shown ; in C, 

the section being to the side of the palicle, the latter is not shown; v, 
ocular vesicle and vitreous humour. 





the secondary 



pouch becomes constricted and closed, and the pouch is soon converted into a shut 
sac, within which the contents subsequently becoming solid form the lens and its 
capsule. After the lens has been separated from the cuticle, the deeper tissue sends a 

o C 



738 



THE EYE. 



projection from below upwards between the lens and the optic vesicle, in such a 
manner as to invaginate the superficial and lower walls of the vesicle, pressing them 
upwards and inwards on the superior and deep walls, and giving them the form of a 
cup imperfect below, the secondary optic vesicle. The involution gives rise to the 




(Fig. 491. DIAGRAMMATIC SKETCH OP A 
VERTICAL LONGITUDINAL SECTION 
THROUGH THE EYEBALL OP A HUMAN 
FCETUS OP FOUR WEEKS (after Kolli- 
ker). 122 

The section is a little to the side so as to 
avoid passing through the ocular cleft, c, 
the cuticle, where it becomes later the 
cornea; I, the lens; op, optic nerve 
formed by the pedicle of the primary optic 
vesicle ; vp, primary medullary cavity or 
optic vesicle ; p, the pigment-layer of the 
choroid coat of the outer wall ; r, the 
inner wall forming the retina ; vs, secon- 
dary optic vesicle containing the rudiment 
of the vitreous humour. 



cavity in which the vitreous humour is formed ; and, the forepart of the optic nerve 
participating in the imagination, it is by this means that the central artery of the 
retina is introduced into the nerve and the eyeball, being, as it were, folded within 
them. The deficiency in the wall of the cup of the secondary vesicle inferiorly is 



Fig. 492. 




Fig. 492. TRANSVERSE VERTICAL SECTION OF THE 
EYEBALL OP A HUMAN EMBRYO OP FOUR WEEKS 
(from Kolliker). *- 

The anterior half of the section is represented. 
pr, the remains of the cavity of the primary optic 
vesicle ; p, the inner part of the outer layer, form- 
ing the choroidal pigment; r, the thickened inner 
part giving rise to the columnar and other struc- 
tures of the retina ; v, the commencing vitreous 
hiimour within the secondary optic vesicle ; v', the 
ocular cleft through which the loop of the central 
blood-vessel, a, projects from below ; l t the lens 
with a central cavity. 



gradually filled up by the growing downwards of the edges, until only a cleft is left, 
which is discernible for a considerable time, and has been named the ocular cleft. The 
history of this cleft is of interest in connection with congenital fissure of the iris 
(coloboma iridis) and the accompanying condition of the choroid membrane. Some 
difference of opinion exists with regard to the subsequent history of the walls of the 
secondary vesicle, but the opinion of Kolliker appears to be well founded, that the 
invaginated layer forms the retina, and the outer part the pigmentary epithelium 
of the choroid. Thus the elements of Jacob's membrane and the hexagonal cells of 
the choroid may be regarded as originally continuous, forming together the epithelial 
lining of the cavity of the primary vesicle ; and the development of nervous tissue 
underneath Jacob's membrane, while none exist beneath the choroidal layer, is a 
circumstance which may be looked upon as analogous to the absence of nervous tissue 
from various parts of the walls of the cerebral vesicles. The sclerotic coat and 
cornea are formed from the surrounding tissue external to the parts of the eye which 
they enclose ; and, according to Kolliker, the vascular part of the choroid is of later 
formation. Still later, in the second month of foetal life, the iris begins to be formed 



DEVELOPMENT OF THE EYE. 



as a septum projecting inwards from the forepart of the choroid coat, between the lens 
and the cornea. 

Fig. 493. 



pa-J, 



Fig. 493. VERTICAL LONGITUDINAL SECTION 
OP THE EYE OF AN EMBRYO CALF (from 
Kolliker). 

c, the cornea ; cc, conjunctiva of the cornea ; 
I, the lens ; y, vitreous humour ; r, retina ; 
p, pigment-layer of the choroid ; s c, com* 
mencement of the sclerotic and choroid coats; 
m, superior and inferior recti muscles ; pa, 
folds of integument forming the commence- 
ment of the upper and lower eyelids. 

The crystalline lens in the foetus is sur- 
rounded by a highly vascular tunic, supplied 
by a branch of the central artery of the 
retina, which passes forwards in the axis of 
the globe, and breaks up at the back of the 
lens into a brush of rapidly subdividing 
branches. The forepart of this tunic, ad- 
herent to the pupillary margin of the iris, 
forms the pupillary membrane by which 
the aperture of the pupil is closed. The 

whole tunic, however, together with the artery which supplies it, becomes atrophied, 
and is lost sight of before birth in the human subject, although in some animals it 
remains for a few days after. According to Kolliker, the anterior chamber is formed 




m sc 



Fig. 494. 



Fig. 494. BLOODYESSELS OF THE CAP- 

SULO-PtJPILLARY MEMBRANE OF A 

NKW-EORN KITTEN, MAGNIFIED (from 
Kolliker). 

The drawing is taken from a prepara- 
tion injected by Tiersch, and shows in 
the central part the convergence of the 
network of vessels in the pupillary 
membrane. 



only a short time before birth by the 
intervention of the aqueous humour be- 
tween the iris and cornea. 

The eyelids make their appearance 
as folds of integument, subsequently to 
the formation of the globe. AY hen 
they have met together in front of 
the eye, their edges become closely 
glued together and they again open 
before birth. 

The lachrymal canal may be regarded as a persistently open part of the fissure 
between the lateral frontal process and maxillary lobe of the embryo (See p 65 and 
fig. 56 B, 4, 6.) 




3 c 2 



740 THE EAR. 



THE EAR. 

THE organ of hearing is divisible into three parts : the external ear, the 
tympanum or middle ear, and the labyrinth or internal ear. The first two 
of these are to be considered as accessories or appendages to the third, \\hich 
is the sentient portion of the organ. 

Fig. 495. 




Fig. 495. DIAGRAMMATIC VIEW FROM BEFORE OF THE PARTS COMPOSING THE ORGAN OF 
HEARING OF THE LEFT SIDE (after Arnold, and from nature). 

The temporal bone of the left side, with the accompanying soft parts, has been 
detached from the head, and a section has been carried through it transversely so as to 
remove the front of the meatus externus, half the tympanic membrane, the upper and 
anterior wall of the tympanum and Eustachian tube. The meatus internus has also been 
opened, and the bony labyrinth exposed by the removal of the surrounding parts of the 
petrous bone. 1, the pinna and lobe ; 2, 2', meatus externus ; 2', membrana tympani ; 
3, cavity of the tympanum ; IV, its opening backwards into the mastoid cells ; between 
3 and 3', the chain of small bones ; 4, Eustachian tube ; 5, meatus internus containing 
the facial (uppermost) and the auditory nerves ; 6, placed on the vestibule of the laby- 
rinth above the fenestra ovalis ; a, apex of the petrous bone ; I, internal carotid artery ; 
c, styloid process; d, facial nerve issuing from the stylo-mastoid foramen; e, mastoid 
process ; /, squamous part of the bone covered by integument, &c. 

THE EXTERNAL EAR. 

In the external ear are included the pinna, the part of the outer ear which 
projects from the side of the head ; together with the meatus or passage which 
leads thence to the tympanum, and is closed at its inner extremity by a 
membrane (membrana tympani) interposed between it and the middle ear. 

THE PINNA. 

Superficial configuration. The general form of the pinna or auricle is con- 
cave, as seen from the outside, to fit it for collecting and concentrating the 
undulations of sound ; it is thrown into various elevations and hollows, to 
which distinct names have been given. The largest and deepest concavity, 



STEUCTUEE OF THE PIXXA. 



741 



a little below the centre of the organ, is called the concha ; it surrounds the 
entrance to the external auditory ineatus, and is unequally divided at its 
upper part by a ridge, which is the beginning of the helix. In front of 
the concha, and projecting backwards over the meatus auditorius, is a 
conical prominence, the tragus, covered usually with hairs. Behind this, 
and separated from it by a deep notch (incisura intertragica), is another 
smaller elevation, the antitragus. Beneath the antitragus, and forming the 
lower end of the auricle, is the lobule, which is devoid of the firmness and 
elasticity that characterise the rest of the pinna. The thinner and larger 
portion of the pinna is bounded by a prominent and incurved margin, the 
helix, which, springing above and rather within the tragus, from the hollow 



Fig. 496. OUTER SURFACE OF THE PINNA OF THE EIGHT 
AURICLE. | 

1, helix ; 2, fossa of the helix ; 3, antihelix ; 4, fossa 
of the antihelix ; 5, antitragus ; 6, tragus ; 7, concha ; 
8, lobule. 



Fu 



\ 




of the concha, surrounds the upper and posterior 
margin of the auricle, and gradually loses itself in 
the back part of the lobule. Within the helix is 
another curved ridge, the antihelix, which, begin- 
ning below at the antitragus, sweeps round the hol- 
low of the concha, forming the posterior boundary 
of that concavity, and is divided superiorly into 
two diverging ridges. Between the helix and the 
antihelix is a narrow curved groove, the fossa of 
the helix (fossa iunominata, scaphoid ea) ; and in 
the fork of the antihelix is a somewhat triangular 
depression, the fossa of the antihelix (fossa triaugu- 
laris vel ovalis). 

Structure. The pinna consists of a thin plat 3 of cartilage and of integu- 
ment, with a certain amount of adipose tissue. It presents also several liga- 
ments and small muscles of minor importance. 

The skin of the, pinna is thin, cbsely adherent to the cartilage, and con- 
tains sebaceous follicles, which are most abundant in the hollows of the con- 
cha and scaphoid fossa. 

The cartilage presents all the inequalities of surface already described as 
apparent on the outer surface of the pinna ; and on its cranial surface exhi- 
bits prominences the reverse of the concha and the fossa of the helix, while 
between these is a depression in the situation of the antihelix. This cartilage 
is not confined to the pinna, but enters likewise into the construction of the 
outer part of the external auditory canal. When dissected separate from 
other structures, it is seen to be attached by fibrous tissue to the rough and 
prominent margin of the external auditory meatus of the temporal bone. 
The tubular part is cleft in front from between the tragns and fore part of 
the helix inwards to the bone, the deficiency being filled with fibrous inem- 
"brane ; thus the cartilage may be said to be a plat^, a part of which assumes 
the tubular form by being folded so as to bring the upper margin, which lies 
in front of the tube of the ear, nearly into contact with the lower part, 
which being coiled inwards upon itself forms the upper border of the tragus. 
Following the free border of the plate backwards beneath the meatus, it is 
seen to pass round the lower margin of the concha, and to form the promi- 
nences of the tragus and antitragus, while the cartilage is absent altogether 



742 



THE EAR. 



from the lobule, which contains only fat and tough connective tissue. 
Behind the antitragus is a deep notch, separating it from the cartilage of the 
helix, which here forms a tail-like process descending towards the lobule. At 
the fore part of the pinna, opposite the first bend of the helix, is a small 
conical projection of the cartilage, called the process of the, helix, to which 
the anterior ligament is attached. Behind this process is a short vertical 
slit in the helix ; and on the surface of the tragus is a similar but somewhat 
longer fissure. A deep fissure passes back between the commencement of 
the helix and the tube of the ear, and another passing outwards and 
backwards from the deep end of the longitudinal cleft separates the part 
forming the tragus from the rest of the tube, so that the tube is continuous 
with the pinna only by means of a narrow isthmus. One or two other 
irregular gaps or fissures partially divide the cartilaginous tube transversely, 
and the whole of these deficiencies are termed fissures of Santorini. The 
substance of the cartilage is very pliable, and is covered by a firm fibrous 
perichondrium. 

Of the ligaments of the pinna, the most important are two, which assist 
in attaching it to the side of the head. The anterior ligament, broad and 
strong, extends from the process of the helix to the root of the zygoma. 
The posterior ligament fixes the back of the auricle (opposite the concha) to 
the outer surface of the mastoid process of the temporal bone. A few fibres 
attach the tragus also to the root of the zygoma. Ligarnentous fibres are 
likewise placed across the fissures and intervals left in the cartilage. 

Of the muscles of the pinna, those which are attached by one end to the 
side of the head, and move the pinoa as a whole, have been already des- 
cribed (p. 170) : there remain to be examined several smaller muscles, com- 
posed of thin layers of pale fibres, which extend from one part of the pinna 
to another, and may be named the special muscles of the organ. Six small 
muscles are distinguished ; four being placed on the outer and two on the 
inner or deep surface of the pinna. 

The smaller muscle of the helix (m. minor helicis) is a small bundle of 
oblique fibres, lying over, and firmly attached to, that portion of the helix 

which springs from the 
Fig. 497 Fig. 498. bottom of the concha. 

Fig. 497. CARTILAGE OF THE 
PlNNA EXPOSED, WITH THE 
MUSCLES ON ITS OUTER SUR- 
FACE. 

] , musculus helicis minor ; 
2, m. helicis major ; 3, tra- 
gicus ; 4, antitragicus. 

Fig. 498. INNER SURFACE OF 
THE CARTILAGE OF THE 
PINNA WITH THE SMALL 
MUSCLES ATTACHED. 

5, transversus auriculse 
muscle ; 6, obliquus auriculas 
muscle. 




The greater muscle of the helix (m. major helicis) lies vertically along the 
anterior margin of the pinna. By its lower end it is attached to the process 
of the helix j and above, its fibres terminate opposite the point at which the 
ridge of the helix turns backwards. 



EXTERNAL AUDITORY CANAL. 743 

The muscle of the tragus (m. tragicus) is a flat bundle of short fibres 
covering the outer surface of the tragus : its direction is nearly vertical. 

The muscle of the antitragus (in. autitragicus) is placed obliquely over the 
antitragus and behind the lower part of the antihelix. It is fixed at one 
end to the antitragus, from which point its fibres ascend to be inserted into 
the tail-like extremity 'of the helix, above and behind the lobule. 

The transverse muscle (m. transversus auriculas) lies on the inner or cranial 
surface of the pinna, and consists of radiating fibres which extend from the 
back of the concha to the prominence which corresponds with the groove of 
the helix. 

The oblique muscle (Tod) consists of a few fibres stretching from the back 
of the concha to the convexity directly above it, across the back of the 
inferior branch of the antihelix, and near the fibres of the transverse muscle. 

Arteries r>f the pinna. The posterior auricular artery, a branch from the external 
carotid, is distributed chiefly on the posterior or inner surface, but sends small branches 
round and through the cartilage to ramify on the outer surface of the pinna. Besides 
this artery, the auricle receives others, the anterior auricular from the temporal in 
front, and a small artery from the occipital behind. 

The vei)is correspond much in their course with the arteries. They join the tem- 
poral vein, and their blood is returned therefore through the external jugular. 

Nerves of the pinna. The great auricular nerve (p. 638), from the cervical plexus, sup- 
plies the greater part of the back of the auricle, and sends small filaments with the pos- 
terior auricular artery to the outer surface of the lobule and the part of the ear above it. 
The posterior auricular nerve, derived from the facial (p. 612), after communicating with 
the auricular branch of the pneumogastric, ramifies on the back of the ear and supplies 
the retrahent muscle. The upper muscles of the auricle receive their supply from the 
temporal branches of the same nerve. The auriculo-temporal branch of the third 
division of the fifth nerve (p. 606) gives filaments chiefly to the outer and anterior 
surface of the pinna. 

THE EXTERNAL AUDITORY CANAL. 

The external auditory canal (meatus auditorius externus) extends from 
the bottom of the concha to the membrane of the tympanum, and serves to 
convey to the middle chamber of the ear the vibrations of sound collected 
by the auricle. The canal is about one inch and a quarter in length. In 

Fig. 499. VIEW OP THE LOWER HALF OF THE Fig. 499. 

AURICLE AND MEATUS IN THE LEFT EAR 

DIVIDED BY A HORIZONTAL SECTION (after 

Sommerring). 

1 and 2, cut surfaces of the bony part of the 
meatus ; 3, cut surface of the cartilage of the 
pinna ; 4, external meatus with the openings of 
numerous ceruininous glands indicated ; 5, lobule ; 
6, membrane of the tympanum j 7, dura mater 
lining the skull. 

its inward course it is inclined somewhat 
forwards ; and it presents likewise a dis- 
tinct vertical curve, being directed at fir^t 
somewhat upwards, and afterwards turning 
somewhat abruptly over a convexity of 
the osseous part of its floor, and dipping 

downwards to its termination, a change of direction which must be 
borne in mind by the surgeon in introducing specula into the ear. The 




7-H THE EAR. 

calibre of the passage is smallest about the middle. The outer opening 
is largest from above downwards, but the tympanic end of the tube 
is slightly widest in the transverse direction. At the inner extremity the 
tube is terminated by the membrana tympani, which is placed obliquely, 
with the inferior margin inclined towards the mesial plane, and thus the 
floor of the meatus is longer than its roof. 

The meatus is composed of a tube partly cartilaginous and partly osseous, 
and is lined by a prolongation of the skin of the pinna. 

The cartilaginous part of the meatus forms somewhat less than half the 
length of the passage. It is formed by the deep part of the cartilage of the 
pinna, which has been already described. 

The osseous portion of the meatus is a little longer and rather narrower 
than the cartilaginous part. At its inner end it presents a narrow groove, 
which extends round the sides and floor of the meatus, but is deficient 
above ; into this the margin of the membrana tympani is inserted. 

The skin of the meatus is continuous with that covering the pinna, but is 
very thin, aod becomes gradually thinner towards the bottom of the pas- 
sage. In the osseous part of the canal it adheres very closely to the 
periosteum ; and at the bottom of the tube this lining is stretched over the 
surface of the membrana tympani, forming the outer layer of that struc- 
ture. After maceration in water, or when decomposition is advanced, the 
epidermic lining of the passage may be separated and drawn out entire, and 
then ib appears as a small tube closed at one end somewhat like the finger 
of a glove. Towards the outer part the skin possesses flue hairs and seba- 
ceous glands ; and in the thick subdermic tissue over the cartilage are many 
small oval glands of a brownish-yellow colour, agreeing in form and struc- 
ture with the sweat glands. The cerumen or ear-wax is secreted by these 
glands, glandulce ceruminosce, and their numerous openings may be seen to 
perforate the skin of the meatus. These accessory parts are absent over the 
bony part of the tube. 

Vessels and nerves. The external auditory meatus is supplied with arteries from 
the posterior auricular, internal maxillary and temporal arteries; and with nerves 
chiefly from the temporo-auricular branch of the fifth nerve. 

State in the infant. The auditory passage is in a very rudimentary state in the 
infant, for the osseous part begins to grow out of the tympanic bone only at the period 
of birth (p. 68), and thus the internal and middle parts of the ear are brought much 
closer to the surface than in the adult. 



THE MIDDLE EAR OR TYMPANUM. 

The tympanum or drum, the middle chamber of the ear, is a narrow 
irregular cavity in the substance of the temporal bone, placed between the 
inner end of the external auditory canal and the labyrinth. It receives the 
atmospheric air from the pharynx through the Eustachiau tube, and con- 
tains a chain of small bones, by means of which the vibrations communicated 
from without to the membrana tympani are in part conveyed across the 
cavity to the sentient part of the internal ear, and by which also pressure 
is maintained on the contents of the internal ear, varying in amount accord- 
ing to the tension of the membrana tympani. The tympanum contains 
likewise minute muscles and ligaments, which belong to the bones referred 
to, as well as some nerves which end within this cavity, or pass through it to 
other parts. 

The cavity of the tympanum may be considered as presenting for con- 



CAVITY AND MEMBRANE OF THE TYMPANUM. 745 

sideration a roof and a floor, an outer and an inner wall, and an anterior 
and a posterior boundary. 

The roof of the tympanum is formed by a thin plate of bone, which may 
be easily broken through so as to obtain a view of the tympanic cavity from 
above ; it is situated on the upper surface of the petrous portion of the 
temporal bone, near the angle of union with the squamous portion, from 
which in its development it is derived. 

The floor is narrow, in consequence of the outer and inner boundaries 
being inclined towards each other. 

The outer wall is mainly formed by a thin semitransparent membrane 
mernbrana tympani, which closes the inner end of the external auditory 
meatus ; and, to a small extent, by bone. Immediately in front of the ring 
of bone into which the membrana tympani is inserted, is the inner extremity 
of the fissure of G laser, which gives passage to the laxator tympani muscle, 
and attachment to the processus gracilis of the malleus. Close to the back of 
this fissure is the opening of a small canal (named by Cruveilhier the canal 
of Huguier), through which the chorda tympani nerve usually escapes from 
the cavity of the tympanum and the skull. 

Fig. 500. MEMBRANA TYMPANI Ficr 500 

AS SEEN FROM THE OUTER 
AND INNER SIDE. 

A, the outer surface ; B, the 
inner ; in the latter the small 
bones are seen adherent to the 
membrane and adjacent parts of 
the temporal bone ; in A,- the 
shaded part indicates the small 
bones as partially seen through 
the membrane ; 1, membrana 
tympani ; 2, malleus ; 3, stapes ; 
4, incus. 

The membrana tympani is a nearly circular disc, slightly concave on its 
outer surface. It is inserted into the groove already noticed at the end of 
the meatus externus, and so obliquely that the membrane inclines towards 
the anterior and lower part of the canal at an angle of about 45. The 
handle of the malleus, one of the small bones of the tympanum, descends 
between the middle and inner layers of the membrana tympani to a little 
below the centre, where it is firmly fixed ; and, as the direction of this 
process of the bone is slightly inwards, the outer surface of the mem- 
brane is thereby rendered concave, being held inwards in the shape of a 
shallow cone. 

Though very thin, the membrana tympani is composed of three distinct 
structures. A prolongation of the skin of the external meatus forms the 
outer layer ; the mucous membrane lining the cavity of the tympanum 
furnishes an inner layer ; and between those two is the proper substance of 
the membrane, made up of fine fibrous and elastic tissues with vessels and 
nerves. The greater number of the fibres radiate from near the centre at 
the attachment of the handle of the malleus ; but close to the circumfer- 
ence are some circular fibres, which form a dense, almost ligamentous ring. 

The inner watt of the tympanum, which separates it from the internal ear, 
is very uneven, presenting several elevations and foramina. Near its upper 
part is an ovoid, or nearly kidney-shaped opening fenestra ovalis, which 
leads into the cavity of the vestibule. This opening, the long diameter of 





746 



THE EAR. 



which is from before backwards, with a slight inclination downwards in 
front, is occupied in the recent state by the base of the stapes, and the 
annular ligament connected with that process of bone. Above the fenestra 
ovalis, and between it and the roof of the tympanum, a ridge indicates 
the position of the aqueduct of Fallopius, as it passes backwards, contain- 
ing the portio dura of the seventh nerve. Below it is a larger and more 
rounded elevation, caused by the projection outwards of the first turn of 
the cochlea, and named the promontory, or tuber cochleae ; it is marked by 
grooves, in which lie the nerves of the tympanic plexus. 

Fig. 501. 




Fig. 501. INNER WALL OP THE OSSEOUS TYMPANUM AS EXPOSED BY A LONGITUDINAL 
SECTION OP THE PETROUS AND MASTOID BONE (from Gordon). 

1, opening of the tympanum into the inastoid cells ; 2, fenestra ovalis ; 3, fenestra 
rotunda ; 4, promontory ; 5, aqueduct of Fallopius, or canal of the facial nerve ; 6, 
junction of the canal for the chorda tympani with the aqueduct ; 7, processus cochleari- 
formis ; 8, groove above it for the tensor tympani muscle ; 9, Eustachian tube j 10, 
anterior orifice of the carotid canal. 

Below and behind the promontory, and somewhat hidden by it, is a 
slightly oval aperture named fenestra rotunda) which lies within a funnel- 
shaped depression. In the macerated and dried bone the feuestra rotunda 
opens into the scala tympani of the cochlea ; but, in the recent state it is 
closed by a thin membrane. 

The membrane closing the fenestra rotunda the secondary membrane of 
the tympanum (Scarpa) is rather concave towards the tympanic cavity, 
and is composed of three strata like the membrana tympani ; the middle 
layer being fibrous, and the outer and inner derived from the membranes 
lining the cavities between which it is interposed, viz., the tympanum and 
the cochlea. 

The posterior wall of the tympanum presents at its upper part one larger, 
and several smaller openings, which lead into irregular cavities, the mastoid 
cells, in the substance of the mastoid process of the temporal bone. These 
cells communicate freely with one another, and are lined by mucous mem- 
brane continuous with that which clothes the tympanum. Behind the 
fenestra ovalis, and directed forwards, is a small conical eminence, called 
the pyramid, or eminentia papillaris. Its apex is pierced by a foramen, 
through which the tendon of the stapedius muscle emerges from a canal 
which turns downwards in the posterior wall of the tympanum, and joins 
obliquely the descending part of the aqueduct of Faliopius. 



THE EUSTACHIAN TUBE. 747 

The anterior extremity of the tympanum is narrowed by the gradual 
descent of the roof, and is continued into the Eustachiau orifice. The 
lower compartment of this orifice, lined with mucous membrane, forms the 
commencement of the Eustachian tube ; the upper compartment, about 
half an inch long, lodges the tensor tympaui muscle, and opens into the 
tympanum immediately in front of the feuestra ovalis, surrounded by the 
expanded and everted end of the cochleariforrn process, which separates it 
from the lower compartment. 

Fig. 502. 




Fig. 502. ANTERO-POSTEKIOR SECTION OP THK TEMPORAL BONE, SHOWING THE INNER 
WALL OF THE TYMPANUM, wna THE EUSTACHIAN TUBE AND SMALL BONES IN THE 
RECENT STATE (from Arnold). 

1, styloid process ; 2, mastoid process ; 3, tipper part of the petrous bone ; 4, pharyn- 
geal end of the Eustachian tube ; 5, its cartilage ; 6, its mucous surface ; 7, carotid 
caual ; 8, fenestra rotunda; 9, malleus; 10, incus; 11, stapes; 12, pyramid and 
stapedius muscle ; above 9, and behind 10, the suspensory ligaments of the malleus a ;d 
incus are also seen. 

The Eustachian tube is a canal, formed partly of bone, partly of cartilage 
and membrane, which leads from the cavity of the tympanum to the upper 
part of the pharynx. From the tympanum it is directed forwards and 
inwards, with a little inclination downwards ; and its entire length is about 
an inch and a half. The osseous division of the Eustachian tube, already 
described in the Osteology, is placed in the angle of junction of the petrous 
portion of the temporal bone with the squamous portion. The anterior 
part of the tube is formed of a triangular piece of cartilage, the edges of 
which are slightly curled round towards each other, leaving an interval at 
the under side, in which the canal is completed by dense but pliable fibrous 
membrane. Narrow behind, the tube gradually expands till it becomes 
wide and trumpet-shaped in front ; and the anterior part is compressed 
from side to side, and is fixed to the inner pterygoid process of the sphenoid 
bone. The anterior opening is oval in form, and is placed obliquely at 
the side and upper part of the pharynx, into which its prominent margin 
projects behind the lower meatus of the nose, and above the level of the 
hard palate. Through this aperture the mucous membrane of the pharynx 
is continuous with that which lines the tympanum, and under certain, 
conditions air passes into and out of that cavity. 



748 



THE EAB. 



SMALL BONES OF THE EAR. 



Three small bones (ossicula auditus) are contained in the uppr-r part of 
the tympanum : of these, the outermost (malleus) is attached to the mein- 
brana tympani j the innermost (stapes) is fixed in the fenestra oveilis ; and 



Fig. 503. 




Fig. 503. BONES OP THE TYMPANUM 
OF THE RIGHT SIDE (from Arnold), f 

A, malleus; 1, its head; 2, the 
handle ; 3, long or slender process ; 4, 
short process ; B, incus ; 1, its body ; 
2, the long process with the orbicular 
process ; 3, short or posterior process ; 
4, articular surface receiving the head 
of the malleus; C, stapes; 1, hea4 ; 
2, posterior crus ; 3, anterior crus ; 
4, base ; C*, base of the stapes ; D, 
the three bones in their natural con- 
nection as seen from the outside ; a, 
malleus ; b, incus ; c, stapes. 

the third (incus), placed between 
the other two, is connected to 
both by articular surfaces. The 
malleus and incus are placed in 
nearly a vertical, the stapes in a 
horizontal direction. They form 

together an angular and jointed connecting rod between the membrana 
tympani and the membrane which closes the fenestra ovalis. 

The malleus, or hammer bone, consists of a central thicker portion, with 
processes of different lengths. At the upper end of the bone is a rounded 
head (capitulum), which presents internally and posteriorly an irregularly 
oval surface covered with cartilage, for articulation with the incus. Below 
the head is a constricted neck (cervix); and beneath this another slight 
enlargement of the bone, to which the processes are attached. The handle 
(manubrium) of the malleus is a tapering and slightly twisted process, com- 
pressed from before backwards to near its point, where it is flattened in the 
opposite direction : it descencre with a slight inclination forwards and in- 
wards, and is received between the middle and inner layers of the membrana 
tympani, to which it is closely attached. The long process (processus gra- 
cilis) is a very slender spiculum of bone, which in the adult is usually broken 
off in its removal from the tympanum, in consequence of its union with the 
temporal bone ; it projects at nearly a right angle from the front of the 
neck of the malleus, and extends thence obliquely downwards and forwards 
to the Glasserian fissure. Its end is flattened and expanded, and is con- 
nected by ligamentous fibres and by bone to the sides of the fissure. The 
short process (processus brevis vel obtusus) is a low canical eminence spring- 
ing from the root of the mauubrium, beneath the cervix, and projecting 
outwards towards the upper part of the membrana tympani. 

The incus has been compared to an anvil in form ; but it resembles per- 
haps more nearly a tooth with two fangs widely separated. It consists of 
a body and two processes. The body presents in front a concavo-convex 
articular surface, which is directed upwards and forwards, and receives the 
head of the malleus. The surfaces of the joint thus formed are tipped with 
articular cartilage and enclosed by a synovial membrane. The shorter of 



THE SMALL BOXES AND THEIR MUSCLES. 749 

the two processes (crus breve) of the incus projects nearly horizontally 
backwards from the upper part of the body of the bone, and is connected 
by ligainentous fibres with the posterior wall of the tympanum near the 
entrance of the rnastoid cells. The long process (crus longum) tapers 
rather more gradually, and descends nearly vertically behind the handle of 
the malleus : at its extremity it is bent inwards, and is suddenly narrowed 
into a short neck ; and upon this is set a flattened rounded tubercle (pro- 
cessus lenticularis), tipped with cartilage. This tubercle, which articulates 
with the head of the stapes, was formerly, under the name of os orbiculare 
sen lenticulare, described as a separate bone, which indeed it originally is in 
childhood. 

The stapes, the third and innermost bone of the ear, is in shape remark- 
ably like a stirrup, and is composed of a head, a base, and two crura. The 
head is directed outwards, and has on its end a slight depression, covered 
with cartilage, which articulates with the lenticular process of the incus. 
The base is a plate of bone placed in the fenestra ovalis, to the margin 
of which it is fixed by ligameutous fibres. The form of the base is 
irregularly oral, the upper margin being curved, while the lower is nearly 
straight. The crura of the stapes diverge from a constricted part (neck) 
of the bone, situated close to the head, and are attached to the outer 
surface of the base near its extremities. The anterior cms is the shorter 
and straighter of the two. The crura, with the base of the stapes, enclose 
a small triangular or arched space, which in the recent state is occupied by 
a thin membrane stretched across. A shallow groove runs round the opposed 
surfaces of the bone, and into this the membrane is received. 

LIGAMENTS AND MUSCLES OF THE TYMPANUM. 

Ligaments. In the articulations of the small bones of the ear with each 
other, the connection is strengthened ly ligainentous fibres which cover the 
synovial membranes. 

The attachment of the bones of the ear to tho walls of the tympanum is 
effected partly by the reflections of the mucous membrane lining that cavity, 
but chiefly by muscles and by the following ligaments. 

The suspensory ligament of the malleus consists of a small bundle of fibres, 
which descends perpendicularly from the roof of the tympanum to the head 
of the malleus. / 

The incus is likewise suspended by a small ligament (the posterior liga- 
ment of the incus), which extends from near the point of the short crus 
directly backwards towards the posterior wall of the tympanum, where it is 
attached near the entrance to the mastoid cells. 

Arnold describes an upper ligament which attaches the incus, near its articulation 
with the malleus, to the roof of the tympanum. It lies close behind the suspensory 
ligament of the malleus. 

The annular or orbicular ligament of the stapes connects the base of the 
bone to the margin of the fenestra ovalis, in which it is lodged. 

Muscles. There are three well-determined muscles of the tympanum. 
Sornmerring describes four, and some authors a larger number ; but the 
descriptions of these last muscles are not confirmed by later research. Of 
the three muscles generally recognised, two are attached to the malleus, and 
one to the stapes. 

The tensor tympani (musculus internus mallei) is the largest of these 
muscles. It consists of a tapering fleshy part, about half an inch in length, 
and a slender tendon. The muscular fibres arise from the cartilaginous 



750 



THE EAR. 



end of the Eustacliian tube and the adjoining surface of the sphenoid bone, 
and from the sides of the upper compartment of the Eustachian orifice. In 



Fig. 504. 




Fig. 504. VIEW OF THE CAVITY 
OF THE EIGHT TYMPANUM FROM 
ABOVE. 

The cavity of the tympanum 
and some parts of the labyrinth 
have been exposed by a horizontal 
section removing the upper part of 
the temporal bone. 1, posterior 
semicircular canal opened ; 2, the 
cavity of the cochlea opened ; 3, 
osseous part of the Eustachian 
tube ; 4, head of the malleus ; 5, 
incus ; 6, stapes, with its base set 
in the fenestra ovalis ; 7, tensor 
tympani muscle ; 8, stapedius. 

this canal the muscle is con- 
ducted nearly horizontally 
backwards to the cavity of 
the tympanum. Immediately 
in front of the fenestra ovalis 
the tendon of the muscle 
bends at nearly a right angle 
over the end of the processus 
cochleariformis as through a 
pulley, and, contained in a 
fibrous sheath, passes out- 
wards to be inserted into the 
inner part of the handle of 
the malleus, near its root. 

The laxator tympani (laxator tympani major of Sommerring) is generally 
believed to be distinctly muscular, but being partly concealed by a band of 
fibrous tissue, doubts are still entertained by some observers as to whether 
the structure known under this name is of a muscular or ligamentous nature. 
Arising from the spinous process of the sphenoid bone, and slightly from 
the cartilaginous part of the Eustachiau tube, it is directed backwards, 
passes through the Glaserian fissure, and is inserted into the neck of the 
malleus, just above the root of the processus gracilis. 

The laxator tympani minor of Sommerring (posterior ligament of the malleus, Lincke) 
is made up of reddish fibres, which are fixed at one end to the upper and back part of 
the external auditory meatus, pass forwards and inwards between the middle and 
inner layers of the membrana tympani, and are inserted into the outer border of the 
handle of the malleus, and the short process near it. Sommerring. Icones Organi 
Auditus Humani, 1801. 

The stapedius is a very distinct muscle, but is hid within the bone, being 
lodged in the descending part of the aqueductus Fallopii and in the hollow 
of the pyramid. The tendon issues from the aperture at the apex of that 
little elevation, and passing forwards, surrounded by a fibrous sheath, is 
inserted into the neck of the stapes posteriorly, close to the articulation of 
that bone with the lenticular process of the incus. 

A very slender spine of bone has been found occasionally in the tendon of the 
stapedius in man : and a similar piece of bone, though of a rounder shape, exists con- 




ACTION OF THE MUSCLES. LINING MEMBRANE. 751 

stantly in the horse, the ox, and other animals. This circumstance is the more inte- 
resting when it is remembered that cartilage occupies the position of the stapedius 
before the muscle is developed. (P. 66 and fig. 528.) 

Actions. The malleus and incus move together round an axis extending backwards 
from the attachment of the processus gracilis of the malleus in the Glasserian fissure 
to the attachment of the short process of the incus posteriorly. The tendon of the 
tensor tympani muscle passing from within to be inserted below that line, pulls the 
handle of the malleus inwards, while the laxator tympani inserted above that line, by 
pulling the head of the bone inwards, moves the handle outwards. The incus, moving 
along with the malleus, pushes the stapes inwards towards the internal ear when the 
membrana tympani is made tight, and withdraws that bone from the fenestra ovalis, 
when the membrana tympaui is relaxed. But the cavity of the inner ear is full of 

Fig. 505. OUTLINE OF THE THREE SMALL BONES OF 
THE LEFT EAR AS SEEN FROM BEFORE. f 

This figure is designed to illustrate the effect of 
the action of the tensor and laxator muscles of the 
tympanic membrane in connection with their relation 
to the axis of rotation of the malleus, a, a', the 
malleus ; 6, the incus seen behind it ; c, the stapes ; 
m, mf, the inner part of the meatus externus closevl 
by the tympanic membrane, of which the posterior 
half is represented ; the axis of rotation of the 
malleus being supposed to pass through a point at 
the root of the processus gracilis, g ; the line t, indi- 
cates the direction and position of the tendon of the tensor tympani pulling the lower 
part of the malleus inwards, the line /, that of the laxator tympani pulling inwards the 
upper half of the malleus. 

liquid ; and its walls are unyielding, except at the fenestra rotunda ; when, there- 
fore, the stapes is pushed inwards the secondary membrane of the tympanum, which 
blocks up the fenestra rotunda, must be made tense by pressure from within. The 
attachment of the handle of the malleus, however, to the membrana tympani allows 
greater freedom of movement to that process than is allowed to the stapes by the 
ligament of its base, and when the movement of the stapes ceases, it is plain that the 
malleus in any movement must rotate on the head of the incus; and hence, probably, 
the necessity of a moveable articulation between tho*e bones. The action of the 
stapedius muscle is obviously to draw the head of the stapes backwards, in doing which 
the hinder end of the base of that bone will be pressed against the margin of the 
fenestra ovalis, while the fore part will be withdrawn from the fenestra. The object 
gained by this movement of the stapes is not sufficiently ascertained; but it is at least 
evident that, if the stapes be pressed inwards by the incus in the action of the tensor 
tympani, the stapedius muscle, if then contracted, will modify the pressure on the 
internal ear. It is conceivable that the stapedius may thus protect the sensitive part 
of the ear to a certain extent from excessive stimulation of the auditory nerve. 

THE LINING MEMBRANE OF THE TYMPANUM. 

The raucous membrane of the tympanum is continuous with that of the 
pharynx through the Eustachian tube, and is further prolonged from the 
tympanum backwards into the mastoid cells. Two folds which cross the 
breadth of the cavity descend from the part of the membrane which lines 
the roof. The anterior fold descends to turn round the tendon of the tensor 
tympani muscle ; the posterior fold passes round the stapes. The malleus 
and incus are invested by the lining of the outer wall of the cavity. The 
mucous membrane which lines the cartilaginous part of the Eustachian tube 
resembles much the membrane of the pharynx, with which it is immediately 
continuous ; it is thick and vascular, and is covered by several layers of 
laminar epithelium with vibratile cilia, and is provided with many simple 
mucous glands which pour out a thick secretion : in the osseous part of the 



752 THE EAR. 

tube, however, this membrane becomes gradually thinner. In the tympa- 
num and the mastoid cells it is paler, thinner and less vascular, and secretes 
a less viscid, but yellowish fluid. The epithelium in the tympanic cavity is 
also ciliated. The cilia, however, are usually absent from the part which 
lines the meinbrana tympani (Kolliker, Handbuch, p. 691). 

THE VESSELS AND NERVES OF THE TYMPANUM. 

The arteries of the tympanum, though xery small, are numerous, and 
are derived from several branches of the external, and from the internal 
carotid. 

The fore part of the cavity is supplied chiefly by the tympanic branch of the internal 
maxillary (p. 356), which enters by the fissure of Glaser. The back part of the 
cavity, including the mastoid cells, receives its arteries from the stylo-mastoid branch 
of the posterior auricular aitery (p. 353), which is conducted to the tympanum by the 
aqueduct of Fallopius. These two arteries form by their anastomosis a vascular circle 
round the margin of the membrana tympani. The smaller arteries of tlie tympanum 
are, the petrosal branch of the middle meningeal, which enters through the hiatus 
Fallopii ; branches through the bone from the internal carotid artery, furnished from 
that vessel whilst in the carotid canal; and occasionally a twig along the Eustacliian 
tube from the ascending pharyngeal artery. 

The veins of the tympanum pour their.contents through the middle meningeal and 
pharyngeal veins, and through a plexus near the articulation of the lower jaw, into the 
internal jugular vein. 

Nerves. The tympanum contains numerous nerves; for, besides those 
which supply the parts of the middle ear, there are several which serve 
merely to connect nerves of different origin. 

The lining membrane of the tympanum is supplied by filaments from the 
plexus (tympanic plexus), which occupies the shallow grooves on the inner 
wall of the cavity, particularly on the surface of the promontory. 

The tympanic plexus is formed by the communications between, 1st, the 
tympanic branch (nerve of Jacobson) from the petrous ganglion of the glosso- 
pharyugeal ; 2nd, & filament from the carotid plexus of the sympathetic ; 3rd, 
a branch which joins the great superficial petrosal nerve, from the Vidian ; 
4th and lastly, the small superficial petrosal nerve, from the otic ganglion. 

Fi S- 506 - Fig. 506. VIEW OP THE TYAIPANIO 

PLEXUS OP NERVES (after Hirschfeld 
and Leveille). 

6, spheno-palatine ganglion ; 7, Vidian 
nerve ; 8, great superficial petrosal 
n?rve ; 9, carotid branch of the Vidian 
nerve ; 10, part of the sixth nerve con- 
nected by twigs with the sympathetic ; 
11, superior cervical ganglion of the 
sympathetic ; 12, carotid branch ; 13, 
facial nerve ; 14, glosso-pharyngeal 
nerve ; 15, nerve of Jacobsou ; 16, its 
twig to the sympathetic ; 17, filament 
to the fenestra rotunda ; 18, filament to 
the Eustachian tube ; 19, filament to the 
fenestra ovalis ; 20, union of external deep petrosal nerve with the lesser superficial 
petrosal ; 21, internal deep petrosal twig uniting with the great superficial petrosal. 

The nerve of Jacobson enters the tympanum by a small foramen near its floor, 
which forms the upper end of a short canal in the petrous portion of the temporal 
bone, beginning at the base of the skull between the carotid foramen and the jugular 




THE INTERNAL EAR. OSSEOUS LABYRINTH. 



753 



fossa. The nerve from the carotid plexus is above and in front of this, and passes 
through the bone directly from the carotid canal. The branch to the great superficial 
petrosal nerve is lodged in a canal which opens on the inner wall of the tympanum in 
front of the fenestra ovalis. The small superficial petrosal nerve also enters at the 
fore part of the cavity beneath the canal for the tensor tympani. 

Nerves to Muscles. The tensor tympani muscle obtains its nerve from, 
the otic ganglion (see fig. 410) ; the laxator tympani is said to be supplied 
by the chorda tympani: and the stapedius is figured by Sommerriug as 
receiving a filament from the facial nerve. 

The chorda tympani is invested by a tubular reflection of the lining mem- 
brane of the tympanum ; its course across the cavity has already been 
described (p. 611). 

THE INTERNAL EAR, OR LABYRINTH. 

The inner, or sensory part of the organ of hearing, is contained in the 
petrous portion of the temporal bone. It consists of a cavity the osseous 
labyrinth hollowed out of the bone, and of the membranous labyrinth con- 
tained within the osseous walls. 



Fig. 507. 



Fig. 507. RIGHT BONY LABYRINTH, VIEWED 
FROM THE OUTER SIDE (after Sb'mmer- 
ring). ^ 

The specimen here represented is pre- 
pared by separating piecemeal the looser 
substance of the petrous bone from the dense 
walls which immediately enclose the laby- 
rinth. 1, the vestibule ; 2, fenestra ovalis ; 
3, superior semicircular canal ; 4, horizontal 
or external canal ; 5, posterior canal ; *, am- 
pullae of the semicircular canals ; 6, first 
turn of the cochlea ; 7, second turn ; 8, 
apex ; 9, fenestra rotunda. The smaller 
figure in outline below shows the natural 
size. 



The osseous labyrinth is incompletely 
divided into three parts, named the 
vestibule, the semicircular canals, and 
the cochlea. They are lined throughout by a thin membrane, within which 
there is a clear fluid named perilymph. 

The membranous labyrinth is contained within the bony labyrinth, and, 
being smaller than it, leaves a space between the two, occupied by the peri- 
lymph just referred to. The membranous structure supports numerous 
minute ramifications of the auditory nerve, and encloses a fluid named the 
endolymph. 




THE OSSEOUS LABYRINTH. 



The vestibule forms a central chamber of the labyrinth, which communi- 
cates in front with the cochlea, behind with the semicircular canals, on the 
outer side with the cavity of the tympanum, and on the inner side with the 
roeatus auditorius interims. The vestibule is irregularly ovoidal in ^hape 
from before backwards, and is slightly flattened or compressed from without 

3 D 



751 



THE EAR. 



inwards : except in the last-mentioned direction, in which it is somewhat 
smaller, it measures about -^th of an inch in diameter. 

The outer wall which separates it from the cavity of the tympanum, is 
perforated by the fenestra ovalis, which in the recent state is closed by the 
base of the stapes and its annular ligament. 

At the fore part of the inner wall is a small round pit, the fovea hemi- 
spherica, pierced with many small holes, which serve to transmit branches of 
the auditory nerve from the internal auditory meatus. This fossa is limited 
behind by a vertical ridge named crista vestibuli or eminentia pyramidalis. 
Behind the crest is the small oblique opening of a canal, the aqueduct of the 
vestibule, which extends to the posterior surface of the bone, and transmits 
a small vein in a tubular prolongation of membrane. 

In the roof is an oval depression, placed somewhat transversely, fovea 
hemi-elliptica, whose inner part is separated by the crest from the hemi- 
spherical fossa. 

At the back part of the vestibule are five round apertures, leading into 
the semicircular canals : and at the lower and fore part of the cavity is a 
larger opening, which communicates with the scala vestibuli of the cochlea 
apertura scalm vestibuli. 

The semicircular canals are three bony tubes, situate above and behind 
the vestibule, into which they open by five apertures, the contiguous ends of 



Fig. 508. 




Fig. 508. VIEW OF THE INTERIOR OF THE 
LEFT LABYRINTH (from Sommerring). ?i 

The bony wall of the labyriuth is removed 
superiorly and externally. 1, fovea hemi- 
elliptica ; 2, fovea hemispherica ; 3, common 
opening of the superior and posterior semi- 
circular canals ; 4, opening of the aqueduct 
of the vestibule ; 5, the superior, 6, the 
posterior, and 7, the external semicircular 
canals; 8, spiral tube of the cochlea (scala 
tyropani) ; 9, opening of the aqueduct of the 
cochlea ; 10, placed on the lamina spiralis 
in the scala vestibuli. 



two of the canals being joined. They 
are unequal in length, but each tube 

is bent so as to form about two-thirds of a circle ; and each presents, at one 
end, a slightly dilated part, called the ampulla. The canals are compressed 
laterally, and measure across about ^th of an inch ; but in the ampulla each 
has a diameter of -j^-th of an inch. 

The canals differ from one another in position with regard to the vestibule, 
in direction, and in length. The superior semicircular canal is vertical and 
transverse ; and, rising above any other part of the labyrinth, its place is 
indicated by a smooth arched projection on the upper surface of the 
bone. The ampullary end of this canal is the anterior, and opens by 
a distinct orifice iuto the upper part of the vestibule ; whilst the oppo- 
site extremity joins the non-dilated end of the posterior semicircular 
canal, and opens by a common aperture with it into the back part of 
the vestibule. The posterior semicircular canal, vertical and longitudinal 
in direction, is the longest of the three tubes: its ampullary end is 
placed at the lower and back part of the vestibule ; and the opposite 
end joins in the common canal above described. The external semi- 



THE OSSEOUS COCHLEA, 



755 



circular canal arches horizontally outwards, and opens by two distinct 
orifices into the upper and back part of the vestibule. This canal is shorter 
than either of the other two : its ampulla is at the outer end, just above the 
fenestra ovalis. 

Fig. 509. 




Fig. 509. VIEWS OF A CAST OP THE INTERIOR OP THE LABYRINTH (from Henle). f 

Such casts may easily be marie in fusible metal, and give a very correct view of the 
form of the different parts of the labyrmthic cavity. A, view of the left labyrinth from 
the outer side ; B, the right labyrinth from the inner side ; C, the left labyrinth from 
above ; s, the superior, p, the posterior, and e, the external semicircular canals ; a, their 
several ampullae ; re, fovea hemi-elliptica of the vestibule ; rs, fovea hemispherica ; av, 
aqueduct of the vestibule ; fo, fenestra ovalis ; fr, fenestra rotunda ; c, the coiled tube 
of the cochlea ; c', the first part of the tube towards the base with the tractus forami- 
nosus spiralis. 

The cochlea is the most anterior division of the internal ear. When the 
dense bony substance, in which it lies embedded, is picked away, the 
cochlea presents the form of a blunt cone, the base of which is turned 
towards the internal auditory meatus, whilst the apex is directed outwards, 
with an inclination forwards and downwards, and is close to the canal for the 
tensor tympani muscle. It measures about a quarter of an inch in length, 
and the same in breadth at the base. The osseous part of the cochlea con- 
sists of a gradually tapering spiral tube, the inner wall of which is formed 
by the central column, or modiolus, round which it 
winds, and which is partially divided along its whole 
extent by a spiral lamina, projecting into it from the 
modiolus. From this osseous spiral lamina membranous 
structures are stretched across to the outer wall of the 
tube, and thus are completely separated two passages 
or scalee, oce on each side of the spiral lamina, which 
communicate one with the other by only a small open- 
ing, named helicotrema, placed at the apex of the 
cochlea. 

Fig. 510. OSSEOUS LABYRINTH OF THE BARN-OWL (SiRix 
FLAMMEA) (from Breschet). * 



Fig. 510. 




1, semicircular canals ; 2, vestibule ; 
of a short straight tube. 



cochlea in the form 



That the cochlea is justly to be considered as an elongated tube, coiled 
srirally on the modiolus, is illustrated by the simple pouch-like form of the 
rudimentary cochlea of birds. 

The spiral canal of the cochlea is about an inch and a half long, and 
about the tenth of an inch in diameter in its widest part at the commence- 

3 D 2 



756 THE EAR. 

ment. From this point the canal makes two turns and a half round the 
central pillar (from left to right in the right ear, and in the opposite 
direction in the left ear), and ends by an arched and closed extremity called 
the cupola, which forms the apex of the cochlea. The first coil, being much 
the widest in its curve and composed of the largest portion of the tube, 
nearly hides the second turn from view ; and bulging somewhat into the 
tympanum, forms the round elevation on the inner wall of that cavity called 
the promontory. 

Fig. 511. 





Fig. 511. DIAGRAMMATIC VIEW OF THE CANAL OF THE COCHLEA LAID OPEN, f 

1, modiolus or central pillar; 2, placed on three turns of the lamina spiralis ; 3, scala 
tympani ; 4, scala vestibuli. 

Fig. 512. VIEW OF THE OSSEOUS COCHLEA DIVIDED THROUGH THE MIDDLE 
(from Arnold), f 

. 1, central canal of the modiolus ; 2, lamina spiralis ossea ; 3, scala tympani ; 4, scala 
vestibuli ; 5, porous substance of the modiolus near one of the sections of the canalis 
spiralis modioli. 

The modiolus (columella cochleae) forms the central pillar or axis round 
which turn the spiral tube and the spiral lamina. It is much thickest 
within the first turn of the cochlea, and rapidly diminishes in size in the 
succeeding parts. The outer surface is dense, being, iu fact, composed of the 
walls of the spiral tube ; but the centre is soft and spongy as far as the last 
half coil, and is pierced by many small canals, for the passage of the nerves 
and vessels to the lamina spiralis : one of these canals, larger than the rest 
(canalis centralis modioli), runs from the base through the centre of the 
modiolus. 

The lamina spiralis ossea is a thin, flat plate, growing from and winding 
round the modiolus, and projecting into the spiral tube, so as to divide it 
partly into two. Its free margin, which gives attachment in the recent 
state to the membranous septum, or zone, does not reach farther than about 
half of the distance between the modiolus and the outer wall of the spiral 
tube. The osseous lamina terminates close to the apex of the cochlea in a 
hook-like process (hamulus), which partly bounds the helicotrema. 

The lamina is thin and dense towards its free margin ; but near the 
modiolus it is composed of two dense outer plates enclosing a more open 
and spongy structure, in which are numerous small canals, continuous, but 
running at right angles with the canals in the centre of the modiolus. In 
these the nerves and vessels are lodged : they terminate on the inferior or 
tympanic aspect of the lamina, and the line of their orifices forms the tractus 
foraminosus spiralis. Winding round the modiolus, close to the lamina 
spiralis, is a small canal, named by Rosenthal the canalis spiralis modioli. 

The scalce in the osseous cochlea are two in number, distinguished as the 
scala tympani and scala vestibuli. 



THE MEMBRANOUS LABYRINTH. 757 

The scala tympani, the portion of the tube on the basal side of the lamina 
spiralis, commences at the fenestra rotunda, where in the recent state it is 
separated from the tympanum by the secondary metnbrana tympani. Near 
its commencement is the orifice of a small canal aqueductus cochleae,, which 
extends downwards and inwards through the snbstance of the petrous part 
of the temporal bone to near the jugular fossa, and transmits a small vein . 
The surface of the spiral lamina which looks towards this scala is marked 
with numerous transverse striae. The scala vestibuli is rather narrower than 
the scala tympaui in the first turn of the cochlea ; it commences from the 
cavity of the vestibule, and communicates, as already described, with the 
scala tympani at the apex of the modiolus. 

TJie lining membrane of the osseous labyrinth. This is a thin membrane 
(periosteum ?), which closely adheres to the whole inner surface of the 
several parts of the labyrinthic cavity just described. It has no con- 
tinuity with the lining membrane of the tympanum, being stretched 
across the openings of the round and oval fenestrse. It is composed of 
fibres of connective tissue. Its outer surface is rough, and adheres closely, 
like periosteum, to the bone : the inner surface is pale and smooth, is 
covered with a single layer of epithelium, like that of the arachnoid, and 
secretes a thin, slightly albuminous or serous fluid. This secretion, known 
as the liquor Cotunnii, or perilymph, separates the membranous from the 
osseous labyrinth in the vestibule and semicircular canals, occupies the 
cavities of the scala tympani and scala vestibuli in the cochlea, and is 
continued into the aqueducts as far as the membrane lining these passages 
remains pervious. 

THE MEMBRANOUS LABYRINTH. 

Within the osseous labyrinth, and separated from its lining membrane by 
the perilymph, membranous structures exist in which the ultimate ramifi- 
cations of the auditory nerve are spread. In the vestibule and semicircular 
canals these structures have a general resemblance in form to the com- 
plicated cavity in which they are contained. In the cochlea they complete 
the septum between the scalse already mentioned, and enclose a third spiral 
passage, the canalis membranacea, the existence of which has only been 
discovered of late years. The liquid contained within the membranous 
labyrinth is distinguished as endolymph. 

VESTIBULE. The membranous vestibule consists of two closely connected 
sacs, and the parts by which they are united to the membranous semi- 
circular canals and canal of the cochlea. 

The larger of the two sacs, the common sinus or utricle, is of an oblong 
form and slightly flattened from without inwards. It is lodged in tho 
upper and back part of the osseous vestibule, occupying the fovea hemi- 
elliptica. Opposite the crista vestibuli several small branches of the audi- 
tory nerve enter from the foramina in the bone ; and here the walls of the 
common sinus are thicker and more opaque than elsewhere. The extre- 
mities of the membranous semicircular canals terminate in the cavity of 
the common sinus. A small mass of calcareous particles, otoliths or oto* 
conia, is lodged in the wall of the sac. These otoliths are crystals of 
carbonate of lime, and are described as six-sided, and pointed at their extre- 
mities. They are connected with the wall of the sac in a way not yet 
clearly determined. 

The smaller vestibular vesicle, the saccule, is more nearly spherical than 
the common sinus, but, like it, is somewhat flattened. The saccule is situated 



758 THE EAE. 

in the lower and fore part of the cavity of the osseous vestibule, close to 
the opening from the scala vestibuli of the cochlea, and is received into the 
hollow of the fovea hemispherica, from the bottom of which many branches 
of nerve enter. The sacculus appears to have a cavity distinct from that 
of the utricle, but is filled with the like thin and clear fluid, endolymph, and 
contains similar otoconia in its wall. It is prolonged below into a short 
narrow duct, canalis reuniens, which opens abruptly into the membranous 
canal of the cochlea. 

Fig. 513. 
A. B. 





Fig. 513. VIEWS OF THE INTERIOR OF THE RIGHT LABYRINTH WITH ITS MEMBRANOUS 
PARTS AND NERVES (from Breschet). f 

A, the outer wall of the osseous labyrinth in part removed so as to display the mem- 
branous parts within. 1, commencement of the spiral tube of the cochlea ; 2, posterior 
semicircular canal partially opened, showing its membranous canal and ampulla; 3, 
external or horizontal canal entirely opened ; 4, superior canal ; 5, utriculus or common 
sinus with its group of otoliths ; 6, saccule with its otoliths ; 7, placed on the lamina 
spiralis in the commencement of the scala vestibuli ; 7', scala tyrapani ; 8, membranous 
ampulla of the superior semicircular canal ; 9, ampulla of the horizontal, and 10, that 
of the posterior semicircular canal. 

B, membranous labyrinth and nervous twigs detached ; 1, facial nerve in the meatus 
auditorius internus ; 2, anterior division of the auditory nerve giving branches to 5, 8, 
and 9, the utricle and the ampullae of the superior and external canals ; 3, posterior 
division of the auditory nerve, giving branches to the saccule ; 6, posterior ampulla, 10, 
and cochlea, 4 ; 7, the united part of the superior and posterior canals ; 11, the posterior 
extremity of the external canal. 

SEMICIRCULAR CANALS. The membranous semicircular canals are about 
one third the diameter of the osseous tubes in which they are lodged, and 
are dilated into ampullae within the ampullary enlargements of those tubes. 
At the ampullae they are thicker and less translucent than in the rest of 
their extent, and nearly fill their bony cases. That part of each ampulla 
which is towards the concavity of the semicircle of the canal is free ; whilst 
the opposite portion is flattened, receives branches of nerves and blood- 
vessels, and presents on its inner surface a transverse projection, septum 
transversum, which partly divides the cavity into two. The ampullae like- 
wise contain otoliths in their epithelial lib ing. 

Auditory nerve: vestibular division. At the bottom of the meatus audi- 
torius internus the auditory nerve divides into an anterior and a posterior 
branch, which, broken up into minute filaments, pass through the perfora- 
tions of the cribriform plate which separates the meatus from the internal 
ear, and are distributed respectively to the cochlea and vestibule. In both 
branches, as well as in the trunk, there are numerous nerve-cells, appa- 
rently both with and without poles. The vestibular nerve divides into five 
branches, which proceed respectively to the utricle, the saccule, and the 
three ampullse of the semicircular canals : those for the utricle and the 



MINUTE STRUCTURE OF MEMBRANOUS LABYRINTH. 759 

superior and external semicircular canals enter the cavity in a group along 
the crista vestibuli ; the fibrils for the sacculus enter the vestibule by a 
smaller group of foramina, which are situated below those just described, 
and open at the bottom of the fovea hemispherica ; the branch for the pos- 
terior semicircular canal is long and slender, and traverses a small passage 

Fig. 515. 



Fig. 514. 





r 

'" 



Fig. 514. TRANSVERSE SECTION OF ONE OP THE MEMBRANOUS SEMICIRCULAR CANALS 
(from Kolliker). ^ 

This specimen is from the ear of the calf : a, external fibrous layer with interspersed 
nuclei ; 6, homogeneous layer ; c, epithelial lining. 

Fig. 515. AMPULLA OF THE SUPERIOR AND EXTERNAL SEMICIRCULAR CANALS AND PART 
OF THE COMMON SINUS SHOWING THE ARRANGEMENT OF THE NERVES (from Steifen- 
sand) . %- 

1, membranous ampulla of the superior canal ; 2, that of the external canal ; 3, part 
of the common sinus ; 4 and 5, fork-like swellings of the nerves at their ampullar dis- 
tribution ; 6, twig of the auditory nerve spreading in the common sinus. 

in the bone behind the foramina for the nerve of the sacculus. The nerves 
of the ampullae enter the flattened or least prominent side of the ampullaa, 
where they each form a forked swelling, which corresponds with the trans- 
verse septum already described, in the interior of the dilatation. No 
filaments have been fuund extending to any other parts of the semicircular 
canals. 

Microscopic structure. The walls of the common sinus, sacculus and 
membranous semicircular canals are in general semitransparent ; but they 
are thicker and more opaque where nerves and vessels enter. On the 
outer surface is a layer of minutely ramified blood-vessels and loose tissue, 
which contains irregular pigment- cells : within this is a transparent layer, 
faiutly fibrillated, and presenting elongated nuclei when acetic acid is added ; 
lining the interior is an epithelial layer of polygonal nucleated cells. 
The mode of ending of the nerves in the membranous substance of the 
vestibule and semicircular canals is difficult to investigate, on account of 
the minuteness and delicacy of the parts ; for this reason also observers 
have had recourse in great measure to the examination of the vestibule 



760 



THE EAR. 



and semicircular canals in fishes, in which they are of large size. The 
subject still requires further research, but it appears to be pretty certain 
from the observations of Reich, the successive papers of M. and F. E. 
Schultze, and the corroborating observations of Kolliker, that the nerve 
fibres break up in the transparent layer into minute ramifications, which 
enter the epithelium and form between the epithelial cells spindle-shaped 
nucleated bodies with elongated extremities. There have also been ob- 
served long hair-like processes, fila acustica, projecting into the cavity, 
beyond the epithelial surface of the ridge of the ampullse, and likewise 
in the sacs ; and the actual continuity of these hairs with the nerve- 
terminations has been in one instance observed by F. E. Schultze. 
According to Lang the hairs are only the altered remains of a delicate cap 
of tissue on the surface of the epithelium. (Kolliker's Gewebelehre, 4th 
ed., p. 694.) 



Fig. 516. 



Fig. 517. 




Fig. 516. LEFT COCHLEA OP A CHILD SOME WEEKS OLD, opened (from Reichert). a 

The drawing was taken from a specimen which had been preserved in alcohol, and was 
afterwards dried ; the section is made so as to show the lamina spiralis, scalas, and 
cochlear canal in each of the three coils : the membranous spiral lamina is preserved, 
but the appearances connected with the organ of Corti, &c., have been lost from drying. 
/ r, fenestra rotunda with its membrane ; s t, scala tympani ; s v, scala vestibuli ; I s, 
lamina spiralis ; h t hamulus ; c c, canalis cochleae ; d, opening of the aqueductus 
cochleae 

Fig. 517. VERTICAL SECTION OF THE COCHLEA OF A FOETAL CALF (from Kolliker). f 

In this specimen the external wall was ossified, but the modiolus and spiral lamina 
were still cartilaginous ; the section shows in each part of the cochlear tube the two 
scalaa with the intermediate canalis cochleae and lamina spiralis ; the radiating lines in 
the modiolus indicate the passage of the auditory nerves towards the spiral lamina. 

COCHLEA. The membranous cochlea has the form of a three-sided 
tube, the canalis membranacea, interposed between the scala vestibuli 
and the scala tympani. The peripheral wall of this canal is formed by 
part of the osseous cochlea, and on its other sides it is bounded by the 
basilar membrane and membrane of Reissner respectively, while at its 
inner angle is a structure named limbus laminae spiralis, and in its interior 
resting on the basilar membrane, is the organ of Corti with the membrana 
tectoria covering it. Each of these parts requires description. 

The membrana basilaris, or lamina spiralis membranacea, is stretched 
across from the free margin (labium tympanicum) of the osseous lamina to 




MINUTE STRUCTURE OF THE COCHLEA. 761 

the outer part of the spiral canal, lying in the same plane as the osseous 
lamina, and attached peripherally through the medium of a thick structure, 
the spiral ligament. It increases in breadth from the base to the apex of 
the cochlea, while the osseous spiral lamina diminishes in breadth. Thus 
in the first turn of the cochlea this membrane forms about half of the 
breadth of the septum made by it and the osseous lamina ; but towards the 
apex of the cochlea the proportion between the two parts is gradually 
reversed, until, near the helicotrema, the membranous part is left almost 
unsupported by any plate of bone. 

Fig. 518. SECTION THROUGH ONE Fig. 513. 

OP THE COILS OP THE COCHLEA 

(altered from Henle). ^ 

A, the section is made in a 
specimen softened by immersion in 
hydrochloric acid ; S T, scala tym- 
pani ; S V, scala vestibuli ; C C, 
canalis cochleae ; R, membrane of 
Reissner forming its vestibular /J t 
wall ; I so, lamina spiralis ossea ; 
1 1 s to I s p, lamina spiralis mem- 
branacea ; I Is, limbus laminae 
spiralis ; s s, sulcus spiralis ; n c, 
twigs of cochlear nerve ; g s, gang- 
lion spirale ; t, membrana tectoria; 
6, membrana basilaris ; Co, organ 
of Corti ; Isp, ligameutum spirale. 

The limbus lamincz spiralis (denticulate lamina of Todd and Bowman) 
is a thick periosteal development near the edge of the osseous spiral lamina 
on the side which looks towards the vestibular scala. It makes a some- 
what convex elevation, presenting externally a sharp margin which over- 
hangs that to which the basilar membrane is attached, being separated 
from it by a groove. The groove is termed sulcus spiralis, and the margins 
labium vestibulare and labium tympanicum respectively. The membrane of 
Reissner (membrana vestibularis) arises from the inner part of the limbus, 
and extends outwards at a considerable angle with the osseous spiral 
lamina. 

The membrana tectoria (Claudius), or membrane of Corti (Kolliker), has 
been variously described, but, according to the most recent researches, is 
an elastic membrane attached on its one border close to the membrane of 
.Reissner, and on the other by an extremely delicate portion to the peri- 
pheral wall of the cochlea, a little above the membrana basilaris (Claudius 
and Henle). It thus divides the canalis membrauacea into two parts : the 
large part placed between it and the membrane of Reissner, and con- 
taining endolymph ; the other, a narrow interval dividing it from the 
membrana basilaris, and occupied by various cellular and rod-like structures 
of a highly complicated description, which together are designated as the 
organ of Corti. 

The canalis membranacea, or ductus cochlearis, bounded in the manner 
already described, presents a blind pointed extremity at the apex and 
another at the base. That at the apex extends beyond the hamulus, fixed 
to the wall of the cupola, and partly bounding the helicotrema ; that at 
the base fits into the angle at the commencement of the osseous spiral 
lamina in front of the floor of the vestibule. Near to this blind extremity 
the canalis membranacea receives a small duct, canalis reuniens (Hensen), 



762 



THE EAK. 



which is continued downwards from the saccule of the vestibule like the 
neck of a flask, and enters the membranous canal abruptly nearly at a right 
angle to it. Thus the cavity of the canalis membranacea is rendered con- 
tinuous with that of the saccule. 




Fig. 519. THE LEFT LABYRINTH OF 
A CHILD AT BIRTH, PARTIALLY 
OPENED ON ITS OUTER SIDE TO SHOW 
THE COMMENCEMENT OF THE MEM- 
BRANOUS CANAL OF THE COCHLEA 
(slightly altered after Reich ert). f 

The external or horizontal canal has 
been removed; cs, superior canal; cp, 
posterior canal ; a s, membranous am- 
pulla and tube of the superior canal 
cut short ; a 7i, that of the external or 
horizontal canal ; h, undilated end of 
the horizontal canal in front of the 
common opening of the superior and 
posterior canals ; p s, united superior 
and posterior canals ; u, utriculus ; s, eacculus ; c c, vestibular part or commencement 
of the membranous canal of the cochlea ; c r canalis reuniens connecting it with the 
sacculus ; c, cochlea. 

It is necessary to explain that, although the canalis membranacea was described by 
Reissner so long ago as in 1851, yet, owing to some confusion having arisen between 
the membrane of .Reissner and the membrana tectoria described by Corti, whose 
work appeared at the same time, the nature of this canal has until comparatively 

Fig. 520. DISTRIBUTION 
OF THE COCHLEAR 
NERVES IN THE LAMINA 
SPIRALIS (after Henle). 

A, part of the modiolus 
and spiral lamina showing 
the cochlear nerves form- 
ing a network, viewed from 
the base ; 1, the twigs of 
the nerve issuing frem the 
tractus spiralis foramino- 
sus ; 2, the branches of 
the nerve entering by the 
central canal of the modi- 
olus ; 3, wide plexus in 
the bony lamina spiralis ; 
4, close plexus at its 
border ; 1 1, labium tym- 
pauicum; zi, zona interna ; 
z e, zona externa ; 1 8 p, 
ligamentum spirale. 13, 
part of the nerves ex- 
tracted and more highly 
magnified ; 2, twigs of the 
nerve from the modiolus 
close to the lamina spiralis 
ossea ; y s, spiral gangli- 
form enlargement of the 
nerve (habenaria gan- 
glionaris) ; f s, nerve-fibres 

running spirally along the gangliforra swelling (Henle) ; 3, wide plexus ; 4, close plexus 

of nerve -fibres as in A. 




MIXUTE STRUCTURE OF THE COCHLEA. 763 

recently been generally misconceived. The history of the discovery and subsequent 
appreciation of the nature of the canalis membranacea is fully given by Reichert. 
(Abhandl. d. Konigl. Akad. d. Wissensch., Berlin, 1864.) 

Cochlear division of the auditory nerve. The nerve of the cochlea is 
shorter, flatter, and broader than any of the other nerves of the internal 
ear, and perforates the bone by a number of foramina at the bottom of 
the internal rneatus, below the opening of the Fallopian aqueduct. These 
foramina are arranged in a shallow spiral groove (tractus spiralis fora- 
minulentus) in the centre of the base of the cochlea ; and they lead into 
small bony canals, which follow first the direction of the axis of the cochlea, 
through the modiolus, and then radiate outwards, between the plates of 
the bony lamina spiralis. In the centre of the spiral groove is a larger 
foramen which leads to the canalis centralis modiolL Through the central 
foramen and straight canal the filaments for the last half-turn of the 
lamina spiralis are conducted ; whilst the first two turns are supplied by 
filaments which occupy the smaller foramina and bent canals. In the 
bone the nerves have dark outlines, and near the edge of the spiral lamina 
they form a plexus which contains ganglion-cells, and may be considered as 
a spiral ganglion contained in an osseous canal, canalis spiralis modioli, 
already mentioned. From the outer side of this ganglion the fibres, still 
possessing the dark outline, pass onwards with a plexiform arrangement, and, 
emerging from the bone beneath the labium tympanicum of the limbus, 
are collected into bundles, which, opposite a line of perforations situated at 
the junction with the membrana basilaris and named habenula perforata, 
present the appearance of conical extremities entering those perforations. 
Beyond this they have not yet been traced with certainty, although it seems 
probable, as suggested by Kolliker, that the nerves are in continuity with 
spindle-shaped cells in the organ of Corti. 

Microscopic structure. The limlus lamina spiralis is a thick structure 
continuous with the periosteum of the vestibular surface of the osseous 
lamina. Its free surface is thrown into a number of fungiform elevations 
narrower at the base than at their extremities. Towards the inner part 
of the limbus these elevations are short and vertical, but those which are 
placed further out are more and more oblique and longer, and the labium 
vestibulare is formed by the outermost of them, which are lengthened into 
rib-like processes with flat extremities placed edge to edge, overhanging 
the sulcus spiralis like teeth. In the spaces between the elevations numer- 
ous small bodies like nuclei are disposed. In the floor of the sulcus 
spiralis where the labium tympanicum is continued into the membrana 
basilaris a series of elevations (apparent teeth of Corti) are directed into 
the membrane, and between their outer extremities are the oblique perfora- 
tions occupied by the conical extremities of the nerve-bundlea. This part 
is the habenula perforata of Kolliker : it is described by him along with the 
membrana basilaris, and by Henle along with the limbus. Henle considers 
the appearance of elevations as caused merely by the nerve-bundles grooving 
the under surface and leaving thicker structure between. 

The membrana basilaris is divisible into an inner and an outer zone. 
The inner zone (habenula tecta vel arcuata) is covered over by the rods of 
Corti ; the outer zone (zona pectinata) is attached peripherally to the walls 
of the canal through the medium of the cochlear ligament. The inner 
zone, together with the apparatus on its surface, continues, according to 
Henle, of an uniform breadth of about -aj-oth of an inch, both in the dif- 
ferent parts of the same cochlea, and likewise in different animals : so that 



764 THE EAR. 

Fig. 521. 




Fig. 521. UPPER OR YESTIBULAR SURFACE OF A NARROW STRIP OF THE LAMINA 
SPIRALIS MEMBRANACEA (from Kolliker after Corti). 2 -p 

The drawing is defective as regards the organ of Corti, but explains the nomenclature 
of the parts introduced by that author, and more or less adhered to by subsequent writers, 
although variously departed from in some of its details. The nomenclature adopted in the 
text has been selected from various writers, and it will be observed difiers considerably 
from the following : a, periosteum of the zona spiralis ossea ; d w, lamina spiralis mem- 
branacea ; d w', zona denticulata ; d f, habenula sulcata ; d, place where the perios- 
teum thickens ; e, granules in the areolse of the habenula sulcata ; fg, teeth of the first 
series; fffh, sulcus vel semicanalis spiralis; A, its lower wall ; h w, habenula denticu- 
lata; Jim, apparent teeth ; nt, teeth of the second series ; np, inner segments of the 
same; o, swellings with nuclei ; pq and qz, articulating pieces of the same : f, anterior 
segments of the second series ; s s s, three cylindrical cells placed on them ; w, epithelial 
cells placed under the membrane of Corti ; w' w, zona pectinata ; a a, band-like 
elevations of the habenula sulcata ; #, placed where a tooth of the first series takes 
its origin ; 7, holes between the apparent teeth ; 5, fore part of one of the teeth of the 
second series thrown back ; e, one of them in its place without its epithelial cells ; one 
with only the lowest epithelial cell ; i\, one with the two lowest cells ; 8, striae or slight 
elevations of the zona pectinata ; /c, periosteum attaching the lamina spiralis, with A, 
apertures between the bundles. 

the increasing breadth of the membrane from base to apex of the cochlea 
is due to broadening of the zona pectinata. According to the same 
observer the membrane is mainly homogeneous, and in the outer zone is 
thicker than in the inner, and somewhat tuberculated ; but on the surface 
towards the membranous canal it is transversely striated by a layer of 
extremely delicate fibres ; and on the other surface is a less perfect layer 
of fibres with spindle-shaped corpuscles, which are placed longitudinally, 
and in young subjects are arranged so as to cover the inner zone and the 
attachment to the spiral ligament, leaving the outer zone free. A single 
layer of epithelium lies on the surface. 

The ligamentum spirale (musculus cochlearis of Todd and Bowman) is 
triangular in section, receiving at its inner angle the basilar membrane, and 
spreading out rapidly to be attached by a broad base to the wall of the 
cochlea. Its fibres are directed outwards from the membrane to the bone, 
and it exhibits nuclei, like the ciliary muscle, whence Todd and Bowman 
conceived it to be muscular. Hensen represents it as composed of branch- 
ing nucleated cells. 

The organ of Corti. Under this name may be comprised the whole of 
the structures intervening between the membrana basilaris and meinbrana 
tectoria. The most prominent part of it is formed by an outer and an inner 
series of rods, which, attached respectively to the inner and outer margins of 
the inner zone of the basilar membrane, meet together like the beams of a 
roof, and cover in a three-sided space, of which the inner zone of the basilar 
membrane is the floor. These structures, the fibres or rods of Corti, are 
closely adherent by their lower extremities to the basilar membrane. They 
are placed with the regularity of piano keys, and have been likened in con- 



THE ORGAN OF CORTI. 

Fig. 522. 



765 




Fig. 522. DIAGRAMMATIC OUTLINE OP A RADIAL SECTION THROUGH THE LAMINA SPIRALIS 
MEMBRANACEA, ORGAN OF CORTI, &c. (after Kolliker, Heule, and other*). --^ 

This figure may be regarded as a more enlarged and explanatory view of the part of 
fig. 518 representing the organ of Corti : S V, part of the scala vestibuli ; C C, canalis 
cochleae ; S T, scala tympani ; R, membrane of Reissner, forming the partition between 
the scala vestibuli and the canalis cochleae ; I s o, a small part of the lamina spiralis ossea 
cut in the direction of one of the canals transmitting the cochlear nerves, nc; p, perios- 
teum lining the scala tympani ; Us, limbus laminae spiralis, presenting a great thickening 
of the periosteum, in which over the extremity of the osseous spiral lamina is found the 
sulcus spiralis s s, and upon the upper surface of which are the toothed projections ; I v, 
labium vestibulare ; 1 1, labium tympanicum of the sulcus spiralis ; Ivtolsp, the lamina 
spiralis meinbranacea with its contained parts ; mt, membrana tectoria passing from the 
limbus laminae spiralis to the outer wall of the cochlear tube ; mb, membrana basilaris, 
stretched from the labium tympanicum to the outer wall of the cochlear tube, where it 
expands in the ligamentum spirale, I sp ; the part marked by the letters m b, between two 
short dotted lines, forms the zona tecta or z. arcuata ; the part indicated by m b' and between 
the adjacent dotted lines is the zona pectinata ; C, the organ of Corti ; i, the internal rods ; 
e, the external rods ; these are set by their lower flattened ends on the basilar membrane, 
and are articulated together at their upper parts, a, the inner overlapping the outer ; a 
nucleus is seen close to the base of each of the rods close on the basilar membrane ; m r, 
membrana reticularis, stretched to the outer wall of the cochlea, pc; below mr, the cells 
of Corti lying obliquely on the outer rods, and between them the cells of Deiters, and 
between these and the outer wall of the cochlea epithelial cells ; between a and mr, are 
indicated the perforations through which the hair-like terminations of the cells of Corti 
project : the sulcus spiralis is seen filled with cylindrical and other epithelium. 

sistency to cartilage. The inner rods are more closely set and more nume- 
rous than the outer, and appear generally to be of a uniform breadth, 
flattened, and with a nucleiform body placed subjacent to the lower 
extremity. The outer rods are narrow and cylindrical in their shafts, and 
expanded at the lower extremity, which has a nucleiform body subjacent to 
it, as in the case of the inner rods. At their upper ends where they meet 
together, both sets of rods are thickened, and the parts which are in con- 
tact (coins articulaires externes et internes of Corti) have the appearance of 
quadrilateral plates directed outwards so that those of tUe inner row lie 
over those of the outer row, and those of the outer row are bent backwards 
from the direction in which the rods to which they belong are placed. 
From the junction line of the rods there extends outwards an extremely 
delicate network, the lamina reticularis of Kolliker (i. velamentosa, Deiters), 
which, it may be gathered from different accounts, is mainly constructed of 
a layer of squamous cells so disposed as to leave at least three rows of 
large perforations between them, and which are cemented together by a net- 
work of intervening substance which is sometimes detected when the cells are 
not. At its inner margin this lamina is united by flat plates to the inner 



766 



THE EAE. 



series of rods, and by narrow bodies with flattened extremities to the outer 
series : at its outer margin it has not yet been demonstrated that it is 
attached to the wall of the cochlea, although it has been supposed that its 
function might be to give fixity to the rods of Corti. Besides the rods and 
the lamina reticularis the organ of Corti presents various cellular elements. 
Of these the most important are an outer and inner series of cells with stiff 



Fig. 523. 



A. 





Fig. 523 A. VIEW FROM ABOVE OP THE ORGAN OP CORTI AND LAMINA RETICULARIS IN 
THE Ox (from Kolliker). ^ 

a, inner rods or fibres of Corti ; 6, inner ends of the same with the deeper attached 
nuclei ; c, articulating part of the same ; d, clear plates appended, which with others 
from the outer rods form the commencement of the membrana reticularis ; e, outer rods 
or fibres of Covti ; /, their articulating portions ; g, their terminations at the membrana 
basilaris ; h, plates of the outer rods belonging to the membrana reticularis ; i i, 
apparent extension of the ends of the fibres of Corti in the stride of the zona pectinata of 
the basilar membrane ; I, their inner connecting plates ; I', their outer connecting plates ; 
m, %, o, first, second, and third series of perforations ; p, rectangular terminal part of 
the lamina ; q, prolongation of this in the form of fibres upon the large epithelial cells of 
the organ of Corti. 

Fig. 523 B. THE ORGAN OP CORTI OF THE CAT (from Kolliker). 5 -f 

1, the organ of Corti from above ; c, the articulated part of the inner fibres or rods ; 
d, connected plates which form the commencement of the membrana reticularis ; f, 
articulating portions of the outer rods ; /', one of these connected with a filamentous 
process, and presenting granular or punctated contents ; ra, n, o, first, second, and third 
row of perforations, in which the cilia of Corti's cells are represented as dark arched lines ; 
a, inner ciliated cells with ($) their cilia, forming the outermost part of the thick 
epithelium of the sulcus spiralis (7), and which covers the inner fibres (rods) of Corti as 
far as their articulating pails ; 5, outer part of the network of the lamina reticularis ; 
2, a cell of Corti with its hairs, but no visible filamentous appendage ; 3, lateral view of 
the lamina reticularis with the bundles of cilia of the cells of Corti. 



BLOOD-VESSELS OF THE LABYKIXTH. 767 

cilia projecting from their upper extremities. The inner ciliated cells form 
a single row resting on the articulating ends of the inner rods : the outer 
ciliated cells (pedunculated cells of Corti) are placed in three rows external 
to the outer rods, aud are described as attached by pointed extremities to 
the membrana basilaris, and with their ciliated ends opposite the three rows 
of openings in the lamina reticularis ; so that sometimes when the lamina 
is detached the ends of the cells are detached with it. Alternating with 
the outer ciliated cells are the cells of Deiters, which are fusiform and 
prolonged into a thread at each extremity, one passing up to the 
lamina reticularis, and the other down to the outer zone of the membrana 
hasilaris. The upper surface of the remaining part of the basilar membrane 
is covered with hexagonal epithelium-cells. The sulcus spiralis is likewise 
filled with large epithelial cells, which, according to Kolliker, project in a 
swelling distinct from the proper organ of Corti. 

The mode of termination of the nerves, as has been already said, is uncer- 
tain, but minute fibres, consisting of axis-cylinders only, have been traced 
by Deiters into the organ of Corti, and his statements receive some support 
from Kolliker and Henle. These fibres are said to divide into a radiating set 
distributed both above and beneath the rods, and into a spiral set which are 
continued in the longitudinal direction of the canal. 

The membrana tectoria is described by Henle as presenting three zones. 
The inner of these is delicate and presents large openings corresponding to 
elevations of the limbus ; the middle or generally recognised part is formed 
of layers of fibres directed outwards, but yet crossing each other ; and the 
outer part, unrecognised by most observers, is extremely delicate, forming a 
network, the openings in which are elongated in the direction of the canal. 

The membrane of Heissner is an extremely easily torn membrane, on both 
sides of which epithelium has been described. 

On the microscopic anatomy of the cochlea may be consulted Henle's Systematische 
Anatomic ; Kolliker's Gewebelehre, 4th edition ; also the papers of Corti, Claudius, 
Deiters, and Hensen, in Vols., III. VII., X., and XIII. of Siebold and Kolliker's 
Zeitsch. f. Wissensch. Zoologie; and Deiters Untersuchungen liber die Lamina Spiralis 
Membranacea. 

BLOOD-VESSELS OF THE LABYRINTH. 

Arteries. The internal auditory artery, a branch from the basilar, enters 
the internal meatus of the ear with the auditory and facial nerves, and 
at the bottom of that shallow canal divides into vestibular and cochlear 
branches. 

The vestibular branches are distributed to the common sinus, sacculus, 
and semicircular canals, with the branches of nerve which they accompany 
through the bony foramina. At first they ramify on the exterior of the 
membranous labyrinth, and end in capillaries both on the outer surface and 
in the substance of the special glassy layer. The plexus is best marked 
internally near the ending of the nerves. 

The cochlear branches, twelve or fourteen in number, traverse the many 
small canals in the modiolus and bony lamina spiralis, and form in the 
latter a capillary plexus that joins at intervals the vas spirale, to be pre- 
sently described. From this plexus offsets are distributed in the form of a 
fine network on the periosteum, but the vessels do not anastomose across 
the membrana basilaris. The vas spirale is a single, sometimes branched 
vessel which runs along the under surface of the membranous zone, near 
the bone : it is like a capillary in texture,, but larger in size, and is pro- 



768 THE EAR. 

bably venous. On the outer wall of the membranous canal there is a 
specially vascular strip which has received the name of stria vascularis. 

Besides the foregoing vessel, which is the chief artery of the internal ear, 
the stylo-mast oid branch of the posterior auricular, and occasionally the occi- 
pital artery (Jones), send twigs to the vestibule and the posterior semicircular 
canal. 

Veins. The veins of the cochlea issue from the grooves of the cochlear 
axis and join the veins of the vestibule and semicircular canals : these accom- 
pany the arterial branches, and, uniting with those of the cochlea at the base 
of the modiolus, pour their contents into the superior petrosal sinus. 

DEVELOPMENT OF THE EAR. 

In the very young embryo the first rudiment of the ear is seen in the form of a 
small vesicle the primary auditory vesicle lying at the side of the third primary 
cerebral vesicle. It has to a certain extent an appearance similar to that of the 
primary optic vesicle situated further forwards, and was long very naturally supposed 
to be formed like it by a protrusion of the wall of the primary medullary cavity of 
the brain ; but it has latterly been established by various observers that it is pro- 
duced solely by invagination of the integument, and has no original connection 
with the brain. During the third day of incubation it can be seen in the chick, still 
open to the outside, above and behind the second branchial lappet. It soon becomes 
completely closed, and is afterwards developed into the membranous labyrinth. 
The first complication which the vesicle exhibits is by the extension of a process 
upwards and backwards, which remains permanent in the lower vertebrata, but in 
mammals is obliterated, its vestiges remaining in the aqueduct of the vestibule. The 
semicircular canals next appear as elongated elevations of the surface of the primary 
vesicle : the middle portion of each elevation becomes separated from the rest of the 






Fig. 524. OUTLINES SHOWING THE FORMATION OP THE EXTERNAL EAR IN THE FCETUS. 

A, head and upper part of the body of a human foetus of about four weeks (from 
nature). ^ Four branchial plates (the first, forming the lower jaw, is marked 1), and 
four clefts are shown ; the auditory vesicle (a), though closed, is visible from the tran- 
sparency of the parts, and is placed behind the second branchial plate. 

B, the same parts in a human foetus of about six weeks (from Kcker). f The third 
and fourth plates have nearly disappeared, and the third and fourth clefts are closed ; 
the second is nearly closed ; but the first (!') is somewhat widened posteriorly in con- 
nection with the formation of the mealus externus. 

C, human foetus of about nine weeks (from nature), f The first branchial cleft is 
more dilated, and has altered its form along with the integument behind it in connection 
with the formation of the meatus externus and the auricle. 



DEVELOPMENT OF THE EAR. 



769 



vesicle by bending in of its walls under it, and thus the elevation is converted into 
a tube open at each end, which subsequently becomes elongated and presents an 
ampullar dilatation. The cartilage which forms the osseous labyrinth is continuous 
with that of the rest of the primordial cranium. The cartilaginous walls of the 
cavity are united by connective tissue to the vesicle : this connective tissue, according 
to Kolliker, becomes divided into three layers, of which the outer forms the lining 
periosteum, the inner forms the external walls of the membranous labyrinth, while 
the intervening layer swells up into gelatinous tissue, the meshes of which become 
wider and wider, till at last the space is left which ultimately is found containing 
perilymph. 



Fig. 525. 



Fig. 525. LABYRINTH OF THE HUMAN FCETUS OP FOUR 
WEEKS, MAGNIFIED (from Kolliker). 

A, from behind ; B, from before; v, the vestibule ; 
r v, recessus vestibuli, giving rise later to the aqueduct ; 
c s, commencement of the semicircular canals ; a, 
upper dilatation, belonging perhaps to another semi- 
circular canal ; c, cochlea. 



The cochlea appears at first as a prolongation 
downwards from the auditory vesicle, but afterwards 
become tilted forwards. This prolongation of the 
auditory vesicle is the rudimentary canalis mem- 
branacea. Close to it is placed the cochlear nerve, 

with a gangliform extremity. The canal becomes elongated in a spiral direction, and 
the ganglion, which is elongated with it, becomes the ganglion spirale. Between the 
canal and the cartilaginous wall which afterwards surrounds it a large amount of con- 
nective tissue intervenes, and in this the cavities of the scala vestibuli and scala tym- 
pani appear at a later period, precisely as does the space for the perilymph in the 




Fig. 526. 



Fig. 526. TRANSVERSE SECTION OF 
THE COCHLEA IN A FCETAL CALF, 
MAGNIFIED (from Kolliker). 

C, the wall of the cochlea, still carti- 
laginous ; c c, canalis cochleae ; I s, 
placed in the tissue occupying the 
place of the scala vestibuli indicates 
the lamina spiralis ; n, the central 
cochlear nerve ; g, the place of the 
spiral ganglion ; S, the body of the 
sphenoid ; c k, chorda dorsalis. 



vestibule. The modiolus and spiral 
lamina, according to Kolliker, are 
ossified without intervention of car- 
tilage. Within the canalis mem- 
branacea Kolliker finds in the em- 
bryo a continuous epithelial lining, 

thin on the membrane of Reissner and on the outer wall, but forming a thick eleva- 
tion in the position of the rods of Corti, and a larger elevation more internally, filling 
up the sulcus spiralis. On the surface of this latter elevation he observes a transpa- 
rent body, the membrane of Corti. 

With regard to the middle and external ear, it has been already explained at pages 
65 and 66 that the external aperture, the tympanic cavity, and the Eustachian tube, 
are formed in the posterior or upper part of the first branchial cleft, which remains 
open except at the place where the passage is interrupted by the formation of the 
membrana tympani ; and also that the incus and malleus are formed in the first 
branchial lappet from the proximal part of Meckel's cartilage, and the stapes and 
stapedius muscle and the styloid process in the second lappet. It is pointed out by 

3 E 




770 



THE EAR. 



Kolliker that during the whole period of foetal life the tympanic cavity is occupied 
by connective tissue, in which the ossicles are imbedded ; and that only after the 
breathing process is commenced this tissue recedes before an expansion of the mucous 
membrane. The pinna is gradually developed on the posterior margin of the first 
branchial cleft. It is deserving of notice that congenital malformation of the external 
ear, with occlusion of the meatus and greater or less imperfection of the tympanic 



Fig. 527. 



Fig. 527. VIEWS OF THE 
CARTILAGE OP MECKEL 
AND PARTS CONNECTED 
WITH THE FIRST AND 
SECOND BRANCHIAL 
PLATES. 

A (after Kolliker), head 
of a foetus of about eigh- 
teen weeks, showing the 
cartilage of Meckel in con- 
nection with the malleus, 
&c. M, the cartilage of 
Meckel of the right side. 

B (from nature). An 
enlarged sketch explana- 
tory of the above view; z, 
the zygomatic arch ; ma, 
the mastoid process ; mi, 
portions of the lower jaw 
of which the parts near 
the angle and the sym- 
physis have been removed ; 
M, the cartilage of Meckel 
of the right side; M', a 
small part of that of the 
leftside, joiningthe left car- 
tilage at s, the symphysis ; 
T, the tympanic ring ; m, 
the malleus ; i, the incus; 
s, the stapes ; sta, the 
stapedius muscle ; st, the 
styloid process ; p, h, g, the 
stylo -pharyngeus, stylo- 
hyoid and stylo -glossus 
muscles, st-l, stylo-hyoid 
ligament attached to the 
lesser cornu of the hyoid 
bone ; hy, the hyoid bone ; 
tk, thyroid cartilage. In 
A, the head being turned 
somewhat upwards, the 
same parts are shown, to- 
gether with the surround- 
ing muscles, the carotid 
artery, jugular vein, &c. 



apparatus, are observed in connection with abnormal development of the deeper 
parts of the first and second branchial lappets and the intermediate cleft ; while cases 
have been observed of the persistence in the neck of the adult of one or more of the 
branchial clefts situated behind the first. (Allen Thomson, Proceed. Roy. Soc. of 
Edin. 1844, and Edin. Journ. of Med. Sc. 1847.) 




THE XOSE. CARTILAGES. 



771 



THE NOSE. 

The nose is the special organ of the sense of smell. It has also other 
functions to fulfil ; for, communicating freely with the cavities of the 
mouth and lungs, it is concerned in respiration, voice, and taste ; and by 
means of muscles on its exterior, which are closely connected with the 
muscles of the face, it assists in the expression of the different passions and 
feelings of the mind. 



Fig. 528. LATERAL VIEW OF THE CARTILAGES OP Fig. 528. 

THE NOSE (from Arnold), f 

a, rigbt nasal bone ; b, nasal process of the 
superior maxillary bone ; 1, upper lateral cartilage 
or wing-like expansion of the septal cartilage ; 2, 
lower lateral cartilage (outer part) ; 2*, inner part 
of the same ; 3, sesamoid cartilages. 

This organ consists of, first, the anterior 
prominent part, composed of bone and car- 
tilages, with muscles already described, 
which slightly move the cartilages, and two 
orifices, anterior nares, opening downwards ; 
and, secondly, of the two nasal fossae, in 
which the olfactory nerves are expanded. 
The nasal fossae are separated from each 
other by a partition, septum nasi, formed 
of bone and cartilage : they communicate 
at the outer side with hollows in the neigh- 
bouring bones (ethmoid, sphenoid, frontal, 
and superior maxillary); and they open 
backwards into the pharynx through the 

posterior nares. The skin of the nose is studded, particularly in the grooves 
of the alse or outer walls of the nostrils, with numerous small openings, 
which lead to sebaceous follicles. Within the margin of the nostrils there 
is a number of short, stiff, and slightly curved hairs mbrissce, which grow 
from the inner surface of the alse and septum nasi, as far as the place where 
the skin is continuous with the mucous membrane lining the cavity of the 
nose. 




CARTILAGES OF THE NOSE. 

These are the chief support of the outer part of the organ. They occupy 
the triangular opening seen in front of the nasal cavity in the dried skull, 
and assist in forming the septum between the nasal fossoe. There are usually 
reckoned two larger and three smaller cartilages on each side, and one 
central piece or cartilage of the septum. 

The upper lateral cartilages (cartilagines laterales nasi) are situated in the 
upper part of the projecting portion of the nose, immediately below the free 
margin of the nasal bones. Each cartilage is flattened and triangular in 
shape, and presents one surface outwards, and the other inwards towards 

3 E 2 



772 



THE NOSE. 



Fig. 529. 



Fig. 530. 




the nasal cavity. The anterior margin, thicker than the posterior one, 
meets the lateral cartilage of the opposite side above, but is closely united 
with the edge of the cartilage of the septum below ; so closely indeed, that 
by some, as Henle, the upper lateral are regarded as reflected wings of 
the median cartilage. The inferior margin is connected by fibrous mem- 
brane with the lower lateral cartilage ; and the posterior edge is inserted into 

the ascending process of the 
upper maxilla and the free 
margin of the nasal bone. 



Fig. 529. FROKT VIEW OF THE 
CARTILAGES OF THE NOSE (from 
Arnold), f 

a, a', nasal bones ; 1, 1', upper 
lateral cartilages or wing-like ex- 
pansions of the septal cartilage ; 
2, 2', lower lateral cartilages. 

Fig. 530. VIEW OF THE CARTI- 
LAGES OF THE NOSE FROM BE- 
LOW (from Arnold), f 

2, 2', outer part of the lower 
lateral cartilages ; 2*, 2*, inner 
part of the same ; 4, lower edge 
of the cartilage of the septum. 



The lower lateral cartilages (cartilagines alarum nasi) are thinner than the 
preceding, below which they are placed, and are chiefly characterised by their 
peculiar curved form. Each cartilage consists of an elongated plate, so bent 
upon itself as to pass in front and on each side of the nostril to which it 
belongs, and by this arrangement serves to keep it open. The outer 
portion is somewhat oval and flattened, or irregularly convex externally. 
Behind, it is attached to the margin of the ascending process of the upper 
maxilla, by tough fibrous membrane, in which are two or three cartilaginous 
nodules (cartilag. minores vel sesamoidese) ; above, it is fixed, also by fibrous 
membrane, to the upper lateral cartilage, and to the lower and fore part 
of the cartilage of the septum. Towards the middle line it is curved back- 
wards, bounding a deep mesial groove, at the bottom of which it meets with 
its fellow of the opposite side, and continues to pass backwards, forming 
a small part of the columna nasi, below the level of the cartilage of the 
septum. This inner part of the cartilage of the ala is thick and narrow, 
curls outwards, and ends in a free rounded margin which projects out- 
wards towards the nostril. The lower and most prominent portion of the 
ala of the nose, like the lobule of the ear, is formed of thickened skin with 
subjacent tissue, and is unsupported by cartilage. 

The cartilage of the septum has a somewhat triangular outline, and is 
thicker at the edges than near the centre. It is placed nearly vertically 
in the middle line of the nose, and completes, at the fore part, the separation 
between the nasal fossae. The anterior margin of the cartilage, thickest 
above, is firmly attached to the back of the nasal bones near their line of 
junction; and below this it lies successively between the upper and the 
lower lateral cartilages, united firmly with the former and loosely with the 
latter. The posterior margin is fixed to the lower and fore part of the 
central plate of the ethmoid bone ; and the lower margin is received into 



NASAL FOSSAE. 



773 



the groove of the vomer, as well as into the median ridge between the 
superior maxillae. 



Fig. 531. OSSEOUS AND CARTILAGI- 
NOUS SEPTUM OP THE NOSE, SEEN 
FROM THE LEFT SIDE (from Ar- 
nold). 

, right nasal bone ; 5, superior 
maxillary bone ; c, sphenoidal sinus ; 
d, perpendicular plate of the ethmoid 
bone; e, vomer; 2*, inner part of the 
right lower lateral cartilage ; 4, carti- 
lage of the septum. 

This cartilage is the persistent 
anterior extremity of the primor- 
dial cranium. In young subjects 
it is prolonged back to the body 
of the presphenoid bone; and in 
many adults an irregular thin 
baud remains between the vomer 
and the central plate of the 
ethmoid. 



Fig. 531. 




NASAL FOSSAE. 



The nasal fossae, and the various openings into them, with the posterior 
nares, have been previously described as they exist in the skeleton, and the 

Fig. 532. 




Fig. 532. TRANSVERSE VERTICAL SECTION OF TUB NASAL FOSS.E SEEN FROM BEHIND 
(from Arnold). ^ 

1, part of the frontal bone ; 2, crista galli ; 3, perpendicular plate of the ethmoid ; be- 
tween 4 and 4, the ethmoid cells ; 5, right middle spongy bone ; 6, left lower spongy bone; 
7, vomer ; 8, malar bone ; 9, maxillary sinus ; 10, its opening into the middle meatus. 

greater part of that description is also applicable generally to the nose in a 
recent state ; but it is proper to mention certain differences in the form and 



774 THE NOSE. 

dimension of parts, which depend on the arrangement of the lining mem- 
brane, viz. 

Throughout the whole of the nasal fossae it is to be observed that 

First, owing to the thickness of the membrane in question, (which not only lines 
the walls of the fossae, but covers the spongy bones on both sides,) the nasal cavity is 
much narrower in the recent state. Second, in consequence of the prolongations of 
membrane on their free margins, the turbinate bones, and more particularly the 
lower pair, appear in the recent state to be both more prominent, and longer in the 
direction from before backwards, than in the dried skull. Third, by the arrange- 
ment of the mucous membrane round and over the orifices which open into the 
nasal fossae, some of the foramina in the bones are narrowed, and others completely 
closed. 

In the individual parts of the nasal fossae the following particulars are to be 
noticed. 

In the upper meatus, the small orifice which leads into the posterior ethmoidal 
cells is lined by a prolongation of the thin mucous membrane which continues into 
those cavities ; but the spheno-palatine foramen is covered over by the Schneiderian 
membrane, so that no such opening exists in the recent nasal fossa. 

In the middle meatus the aperture of the infundibulum is nearly hidden by an 
overhanging fold of membrane ; it leads directly into the anterior ethmoidal cells, 
and through them into the frontal sinus. Below and behind this, the passage into 
the antrum of Highmore is surrounded by a circular fold of the pituitary membrane, 
(sometimes prominent and even slightly valvular,) which leaves a circular aperture 
much smaller than the foramen in the bony meatus. 

In the lower meatus, the inferior orifice of the nasal duct is defended by one or 
two folds of membrane; and when there are two, the folds are often adapted so 
accurately together as to prevent even air from passing back from the cavity of the 
nose to the lachrymal sac. 

In the roof the apertures in the cribriform plate of the ethmoid bone are closed 
by the membrane, but the openings into the sphenoidal sinuses receive a prolonga- 
tion from it. 

In the Jloor the incisor foramen is in the recent state generally closed. Some- 
times, however, a narrow funnel-shaped tube of the mucous membrane descends 
for a short distance into the canal, but is closed before it reaches the roof of the 
palate. Vesalius, Stenson, and Santorini, believed that this tube of membrane 
opened generally into the roof of the mouth by a small aperture close behind the 
interval between the central incisor teeth. Haller, Scarpa, and, more recently, Jacob- 
son, find that in man it is usually closed, and often difficult of detection. (See 
Cuvier's Report on a paper by Jacobson, " Annales du Museum d'Hist. Naturelle ; " 
Paris, 1811 ; vol. xviii. p. 412.) 

MUCOUS MEMBRANE. 

The pituitary or Schneiderian membrane, which lines the cavities of the 
nose, is a highly vascular mucous membrane, inseparably united, like that 
investing the cavity of the tympanum, with the periosteum and peri- 
chondrium over which it lies. It is continuous with the skin through 
the nostrils ; with the mucous membrane of the pharynx through the pos- 
terior apertures of the nasal fossae ; with the conjunctiva through the nasal 
duct and lachrymal canaliculi ; and with the lining membrane of the several 
sinuses which communicate with the nasal fossae. The pituitary membrane, 
however, varies much in thickness, vascularity, and general appearance in 
these different parts. It is thickest and most vascular over the turbiuato 
bones (particularly the inferior), from the most dependent parts of which it 
forms projections in front and behind, thereby increasing the surface to some 
extent. On the septum nasi the pituitary membrane is still very thick and 
spongy ; but in the intervals between the turbinate bones, and over the 
floor of the nasal fossae, it is considerably thinner. In the maxillary, frontal, 



MUCOUS MEMBEAKB OF THE XOSE. 



775 



and sahenoidal sinuses, and in the ethmoidal cells, the mucous lining mem- 
brane, being very thin and pale, contrasts strongly with that which occupies 
the nasal fossae. 




Fig. 533. OUTER WALL OF THE LEFT NASAL FOSSA, COVERED BY TUB PITUITARY 
MEMBRANE (from Arnold), f 

1, frontal bone ; 2, left nasal bone ; 3, superior maxillary ; 4, body of the sphenoid with 
the sphenoidal sinus ; 5, projection of the membrane covering the upper spongy bone ; 6, 
that of the middle ; 7, that of the lower ; the upper, middle, and lower meatuses are seen 
below the corresponding spongy bones; 8, opening of the Eustachian tube ; 9, depression 
of the lining membrane of the nose in the anterior palatine canal. 

In respect of the characters of the mucous membrane, three regions of 
the nasal fossae may be distinguished. Thus, the region of the nostrils, 
including all the part which is roofed by the nasal cartilages, is lined with 
stratified squamous epithelium ; the remainder of the fossae is divisible 
into two parts, viz. , the olfactory region in which the epithelium is non-ci- 



Fig. 534. 



Fig. 534. VERTICAL SECTION OF A SMALL PORTION op 
THE MEMBRANE OF THE NOSE FROM THE OLFACTORY 
HKGION (from Ecker), ^ 

a, coloured part of the epithelium ; a', nuclei ; 5, 
deeper part containing the olfactory cells and fila- 
ments ; c, connective tissue of the mucous membrane ; 
d, one of the mucous glands : d', its duct; e, twig of 
the olfactory nerve ; c', small twig passing to the 
surface. 

liated and columnar, and the respiratory 
region in which it is ciliated and columnar. 
The membrane in the respiratory part, con- 
sisting of the inferior turbinated and all the 
lower portions of the fossae, is studded with nu- 
merous mucous glands, which are of branched acinated appearance, and open 
by apparent orifices on the surface. These are most numerous about the 
middle and hinder parts of the nasal fossae, and are largest at the back of 
the septum near the floor of the nasal cavity. They are much smaller and 




776 



THE NOSE. 



leps numerous in the meuVbraue lining the several cavities which communi- 
cate with the nasal fossse. 

The olfactory region or that in which the olfactory nerve is distributed, 
includes the upper and middle turbinated parts, and the upper portion 
of the septum. Its mucous membrane is thicker and more delicate in 
consistence than that of the ciliated region, being soft and pulpy. The 
columnar cells on its surface are prolonged at their deep extremities into 
threads, which have been observed to communicate with stellate cells of 
ihe connective tissue. Beneath the columnar cells is a considerable thick- 
ness of densely nucleated tissue, compared by Henle to the cortical brain- 
substance. The glands of this region are numerous ; but are of a more 
simple structure than those in the lower part of the fossae. 

Fig. 535. CELLS AND TERMINAL NERVE-FIBRES 
OP THE OLFACTORY REGION (from Frey after 
Schultze). 

1, from the frog ; 2, from man ; a, epithelial 
cell, extending deeply into a ramified process; 
b, olfactory cells ; c, their peripheral rods ; 
e, their extremities, seen in 1 to be prolonged 
into ciliary hairs ; d, their central filaments ; 3, 
olfactory nerve-fibres from the dog ; a, the 
division into fine fibrillse. 

Olfactory Cells. Intermixed with the 
columnar epithelial cells of the olfactory 
region, and so numerous as to surround 
each of them, are certain peculiar bodies, 
each consisting of a spindle - shaped 
nucleated cell, from which proceed a 
superficial and a deep process. The 
superficial process is a cylindrical or 
slightly tapering thread passing directly 

/7 ^BIKflflMi^! ' mt ' m * ^ ne sur ^ ace ) an d terminating abruptly 
f IfMO at the same level as the epithelial cells 

I '*Wwf^ ^t between which it lies : the deep process 

A I3P1 * s more s l en der an d passes vertically 

invrards. Both processes frequently pre- 
sent a beaded appearance similar to that 
observed in fine nerve - filaments, and 

considered to be of a similar accidental origin. It was suggested by Max 
Schultze, the discoverer of the olfactory cells, and is highly probable, that 
the deep processes are directly continuous with the filaments of the olfactory 
nerve, but the continuity does not appear to have been actually observed. 

The superficial process of the olfactory cell was observed by Schultze to be sur- 
mounted by a short stiff hair-like process, and has been so described by others ; but 
both the discoverer and others are now agreed that this appearance results from the 
coagulation of albumen escaped from the interior of the process. Long and fine hair- 
like processes do, however, exist on the olfactory membranes of amphibia, reptiles, 
and birds, and had been previously pointed out by Schultze. 

Olfactory Nerve. The filaments of this nerve, lodged at first in grooves 
on the surface of the bone, enter obliquely the substance of the Schneiderian 
membrane, and pass to their distribution between its mucous and fibrous 
layers. The nerves of the septum are rather larger than those of the outer 
wall of the nasal fossse ; they extend over the upper third of the septum, 




OLFACTORY KERVE. 



777 



and as they descend become very indistinct. The nerves of the outer wall 
are divided into two groups the posterior branches being distributed over 
the surface of the upper spongy bone, and the anterior branches descending 
ever the plain surface of the ethmoid and the middle spongy bone. 



Fig. 530. 




XT I 



Fig. 536. NERVES OF THE SKPTUJI NASI, SEEN FROM THE RIOHT SIDE (from Sappey 
after Hirscbfeld and Leveille). f 

I, the olfactory bulb ; 1, the olfactory nerves passing through the foramina of the 
cribriform plate, and descending to be distributed on the septum ; 2, the internal or 
septal twig of the nasal branch of the ophthalmic nerve ; 3, naso-palatine nerves. 

The olfactory nerves as they descend ramify and unite in a plexiform 
manner, and the filaments join in brush-like and flattened tufts, which, 
spreading out laterally and communicating freely with similar offsets on 



Fig.' 537. 



Fig. 537. NERVES OF THE OUTER WALLOP 
THE NASAL FOSSJE (from Sappey after 
Hirschfel.l and Leveille). 

1, network of the branches of the olfac- 
tory nerve, descending upon the region of the 
superior and middle turbinated bones ; 2, 
external twig of the ethmoiclal branch of the 
nasal nerve ; 3, spheno-palatine ganglion ; 
4, ramification of the anterior palatine 
nerves ; 5, posterior, and 6, middle divi- 
sions of the palatine nerves ; 7, branch to 
the region of the inferior turbinated bone ; 
8, branch to the region of the superior and 
middle turbinated bones ; 9, naso-palatine 
branch to the septum cut short. 



each side, form a fine net-work 

with elongated and narrow intervals 

between the points of junction ; but 

it is impossible to trace by dissection 

the termination of the nerves in the 

membrane, in consequence of the difficulty of recognising the filaments, 

destitute of dark outline, as they lie among the other nucleated tissues. 

In their nature the olfactory filaments differ much from the fibres of the 
cerebral and spinal nerves : they contain no white substance of Schwann, 




778 



THE NOSE. 



are pale, and finely granular in texture, firmly adherent one to anothef, 
and have oval corpuscles on their surface. 

The greater part of the mucous membrane of the nasal fossse is provided 
with nerves of common sensibility, derived from branches of the fifth pair : 
these have already been described at pp. 599, 603 and 604. 

Blood-vessels. The arteries and veins of the nose are derived from nume- 
rous sources : those of the interior form rich plexuses of capillaries in the 
lining membrane. The description of the arteries will be found at pp. 350, 
356, 361 and 362 ; that of the veins at pp. 456 and 464. 

DEVELOPMENT OP THE NOSE. 

The organ of smell, as was first pointed out by V. Baer, owes its origin, like the 
primary auditory vesicle and the crystalline lens of the eye, to a depression of the 
integument. This depression, the primary olfactory groove, is at first encircled 
by a uniform wall, and is unconnected with the mouth. This stage has been 
observed by Kolliker in the human embryo of four weeks. Soon, hoAvever, by the 
unequal growth of the surrounding parts, a groove is formed, descending from the 
pit and passing into the mouth. Thus the middle frontal process is isolated 
between the grooves of opposite sides, while the lateral frontal process separates 
the nostril from the eye (p. 65). The maxillary lobes, growing forwards from behind 
the eyes, complete the boundaries of the nostrils, which then open into the fore part 
of the mouth. Kolliker observes this stage in the latter half of the second month. 
The palate subsequently grows inwards to the middle line, as has been elsewhere 
stated, and separates the nasal from the buccal cavity ; leaving only the extremely 
minute communication of the incisor foramen. Meanwhile, with the growth of the 
face, the nasal fossae deepen, and the turbinated bones make their appearance as 
processes from their walls. Observations are still wanting to determine whether the 
olfactory nerves are developed from the bulbs, and have thus a cerebral origin, or are 
separately formed from peripheral blastema like all other nerves, with the exception 
of the optic. 

Fig. 537.* 
ABC 






Fig. 537.* VIEWS OP THE HEAD OP HUMAN EMBRTOES, ILLUSTRATING: THE DEVELOPMENT 

OP THE NOSE. 

A, Head of an embryo of three weeks (from Ecker). ] f 1, anterior cerebral vesicle ; 
2, middle vesicle ; 3, nasal or middle frontal process ; 4, superior maxillary process ; 5, 
eye ; 6, inferior maxillary process or first visceral plate, and below it the first cleft j 7, 
8, and 9, second, third, and fourth plates and clefts. 

B, Head of an embryo of about five weeks (from Ecker). ^ 

1, 2, 3, and 5, the same parts as in A ; 4, the external nasal or lateral frontal process, 
inside which is the nasal groove ; 6, the superior maxillary process ; 7, the inferior 
maxilla ; x , the tongue seen within the mouth ; 8, the first branchial cleft which becomes 
the outer part of the meatus auditorius externus. 

C, View of the head of an embryo of eight weeks seen from below, the lower jaw having 
been removed (from Kolliker). | 

?i, the external nasal apertures ; i, intermaxillary or incisor process, and to the outer 
side of this the internal nasal aperture ; m, one of the palatal processes of the upper jaw, 
which advancing inwards from the sides form the partition between the mouth and nose ; 
p, common cavity of the nose, mouth, and pharynx. 



OKGANS OF DIGESTIOX. THE MOUTH. 779 



SECTION VI. SPLANCEDTOLOGY. 

UNDER the division Splanchnology will be described those organs of the 
body which have not found a place in any of the foregoing parts of the 
work. These consist of the organs of digestion, the organs of respiration, 
the urinary organs, and the organs of generation. 

ORGANS OF DIGESTION. 

The digestive apparatus includes that portion of the organs of assimilation 
within which the food is received and partially converted into chyle, and 
from which, after the chyle has been absorbed, the residue or excrement is 
expelled. It consists mainly of a tubular part, the alimentary canal, to- 
gether with various glands of which it receives the secretions. 

The alimentary canal is a long membranous tube commencing at the 
mouth and terminating at the anus, composed of certain tunics or coats, and 
lined by a continuous mucous membrane from one end to the other. Its 
average length is about thirty feet, being about five or six times the length 
of the body. Its upper extremity is placed beneath the base of the skull, 
the succeeding portion traverses the thorax, and by far the greater part is 
contained within the cavities of the abdomen and pelvis. 

The part situated above the diaphragm consists of the organs of mastica- 
tion, insalivation, and deglutition, and comprises the mouthy with the teeth 
and salivary glands, the pharynx, and the oesophagus or gullet. The 
remainder includes that part of the canal which is more immediately en- 
gaged in the digestive process, in absorption, and in defecation, as the 
stomach and the small and large intestine. The glands which are most 
intimately connected with digestion consist of those very numerous smaller 
glandular organs which are situated in the mucous membrane of the alimen- 
tary canal, and the larger glands, such as the pancreas and liver, whose 
ducts open within the canal. 

THE MOUTH. 

The mouth, or, more definitely, the buccal cavity, is the space included 
between the lips and the throat. Bounded by the lips, cheeks, tongue, and 
the hard and soft palate, it communicates behind with the pharynx through 
an opening called the fauces (isthmus faucium). The cavity of the mouth 
is lined throughout by a mucous membrane, which is of a pink rosy hue 
during life, but pale grey after death, and which presents peculiarities of 
surface and structure to be noticed hereafter. 

The lips and cheeks are composed of an external layer of skin, and of a a 
internal layer of mucous membrane, together with muscles, vessels, and 
nerves already fully described in other parts of this work, some areolar 
tissue, fat, and numerous small glands. The free border of the lips is pro- 
tected by a dry mucous membrane, which becomes continuous with the 
skin, is covered with numerous minute papillae, and is highly sensitive. On 
the inner surface of each lip, the mucous membrane forms a fold in the 
middle line, connecting the lip with the gums of the corresponding jaw. 
These are the frcena or frcenula of the lips : that of the upper lip is much 
the larger. 

Numerous small glands, called labial glands, are found beneath the 



780 ORGANS OF DIGESTION. 

mucous membrane of the lips, around the opening of the mouth. They are 
situated between the mucous membrane and the orbicularis oris muscle. 
They are compound glands of a rounded form, the largest of them not ex- 
cseding the size of a split pea ; and they open into the mouth by distinct 
orifices. 

Between the buccinator muscle and the mucous membrane of the cheek, 
by which it is lined in its whole extent, are the buccal glands, similar to the 
labial glands, but smaller. Two or three glands, larger than the rest, found 
between the masseter and buccinator muscles, and opening by separate ducts 
near the last molar tooth, are called the molar glands. The duct of the 
parotid gland also opens upon the inner surface of the cheek, opposite to the 
second upper molar tooth. 

Immediately within the lips and cheek, are the dental arches, consisting 
of the teeth, gums, and maxillse. The jaw-bones, the articulation and move- 
ments of the lower maxilla, and the muscles used in mastication, are else- 
where described. The gums (gingivse) are composed of a dense fibrous 
tissue, connected very closely with the periosteum of the alveolar processes, 
and covered by a red and highly vascular but not very sensitive mucous 
membrane, which is smooth in its general surface, but is beset with fine 
papillae in the immediate vicinity of the teeth. 

THE TEETH. 

In the human subject, as in mammalia generally, two sets of teeth make 
their appearance in the course of life, of which the first constitutes the tem- 
porary, deciduous, or milk teeth, whilst the second is named the permanent 
set. The temporary teeth are twenty in number, ten in each jaw, and the 
permanent set consists of thirty two, sixteen above and sixteen below. 

Deficiencies in the number of the teeth sometimes occur, and the number is frequently 
increased by one or more supernumerary teeth. These are usually small, and pro- 
vided with only a single fang ; and, though generally distinct, they are sometimes 
attached to other teeth : they occur more frequently near the front than the hinder 
teeth, and are more often met with in the upper than in the lower jaw. 

General Characters of the Teeth. Every tooth consists of three portions, 
viz., one which projects above the gums and is named the body or crovin, 
another which is lodged in the alveolus or socket, and constitutes the root 
or fang, and a third, intermediate between the other two, and, from being 
more or less constricted, named the cervix or neck. The size and form of 
each of these parts vary in the different kinds of teeth. 

The roots of all the teeth are accurately fitted to the alveoli of the jaws, 
in which they are implanted. Each alveolus is lined by the periosteum, which 
also invests the contained fang as high as the cervix. This dental perios- 
teum, sometimes named the periodontal membrane, is blended with the 
dense and slightly sensitive tissue of the gums, which closely surrounds the 
neck of the tooth. The roots of all the teeth taper from the cervix to the 
point, and this form, together with the accurate adjustment to the alveolus, 
has the effect of distributing the pressure during use over the whole socket, 
and of preventing its undue action on the apex of the fang through which 
the blood-vessels and nerves enter. 

The thirty-two permanent teeth consist of four incisors, two canines, four 
bicuspids, and six molars in each jaw. The twenty temporary teeth are 
four incisors, two canines, and four molars above and below. There are 



FORM OF PERMANENT TEETH. INCISORS. 



781 



no bicuspids among the temporary teeth, but the eight deciduous molars are 
succeeded by the eight bicuspids of the permanent set. The relative posi- 
tion and arrangement of the different kinds of teeth in the jaws may be 
expressed by the following formula, which also exhibits the relation between 
the two sets in these respects : 



Temporary teeth 



Permanent teeth 



( Upper 
Lower 



MO. CA. IN. CA. MO. 

21412 =10 
. ^^_____ = 20 

21412 =10 



MO. BI. CA. IN. CA. BI. MO. 

Upper 321412 3 = 16 

= 32 



(Lower 321412 3 = 16 



Special Characters of the Permanent Teeth. The incisors, eight in number, 
are the four front teeth in each jaw, and are so named from being adapted 
for cutting or dividing the soft substances used as food. Their crowns are 
chisel-shaped, and have a si arp horizontal cutting edge, which by continued 
use is bevelled off behind in the upper teeth, but in the lower teeth is worn 
down in front, where it comes into contact with the overlapping edges of the 
upper teeth. Before being subjected to wear, the horizontal edge of each 
incisor tooth is serrated or marked by three small prominent points. The 



Fig. 538. 



Fig. 538. INCISOR TEETH OP THE UPPER 
AND LOWER JAWS. 

, front view of the upper and lower 
middle incisors ; 6, front view of the upper 
and lower lateral incisors ; c, lateral view 
of the upper and lower middle incisors, 
showing the chisel shape of the crown ; a 
groove is seen marking slightly the fang 
of the lower tooth ; d, the upper and 
lower middle incisor teeth before they have 
been worn, showing the three pointed pro- 
jections of the cutting edge. 



anterior surface of the crown is 
slightly convex, and the posterior 
concave. The fang is long, single, 
conical, and compressed at the sides, 
where it sometimes though rarely 
presents a slight longitudinal furrow. 

The lower incisor teeth are placed 
vertically in the jaw, but the corre- 
sponding upper teeth are directed 

obliquely forwards. The upper incisors are, on the whole, larger than the 
lower ones. 

In the upper jaw the central incisors are larger than the lateral ; the 
reverse is the case in the lower jaw, the central incisors being there the 
smaller, and being, moreover, the smallest of all the incisor teeth. 

The canine teeth (cuspid ati), four in number, are placed one on each 
side, above and below, next to the lateral incisors. They are larger and 
stronger than the incisor teeth. The crown is thick and conical, convex in 
front and hollowed behind, and may be compared to that of a large incisor 




782 



ORGANS OF DIGESTION. 



tooth the angles of which have been removed, so as to leave a single 
central point or cusp, whence the name cuspidate applied to these teeth. 



this, as 
thrown 



Fig. 539. Fig. 539. CANINE TOOTH OP THE UPPER JAW. 

a, front view ; &, lateral view, showing the long fang grooved 
on the side. 

The point always becomes worn down by use. The 
fang of the canine teeth is single conical, and com- 
pressed at the sides : it is longer than the faDgs of 
any of the other teeth, and is so thick as to cause a 
corresponding prominence of the alveolar arch : on 
the sides it is marked by a groove, an indication, as 
it were, of the cleft or division which appears in 
the teeth next following. 
a The upper canines, popularly called the eye-teeth, 

are larger than the lower, and in consequence of 
well as of the greater width of the upper range of incisors, they are 
a little farther outwards than the lower canine teeth. In the dog- 






Fig. 540. Fig. 541. Fig. 540. FIRST BICUSPID TOOTH OF 

THE UPPER AND LOWER, JAWS. 

a, front view; 5, lateral view, showing 
the lateral groove of the fang, and the 
tendency in the upper to division. 

Fig. 541. FIRST MOLAR TOOTH OF THE 
UPPER AND LOWER, JAWS. 

They are viewed from the outer aspect. 

tribe, and in the carnivora gene- 
rally, these teeth acquire a great 
size, and are fitted for seizing and 
killing prey, and for gnawing and 
tearing it when used as food. 

The bicuspids (bicuspidati), also 
called premolars, are four in each 
jaw ; they are shorter and smaller 
than the canines, next to which 
they are placed, two on each side. 

The crown is compressed before and behind, its greater diameter being 
across the jaw. It is convex, not only on its outer or labial surface, like 
the preceding teeth, but on its inner surface also, which rises vertically 
from the gum : its free extremity is broader than that of an incisor or canine 
tooth, and is surmounted by two pointed tubercles or cusps, of which the 
external one is larger and higher than the other. The fang is also flattened, 
and is deeply grooved in all cases, showing a tendency to become double. 
The apex of the fang is generally bifid, and in the first upper bicuspid the 
root is often cleft fora considerable distance; but the bicuspid teeth are very 
variable in this respect, and may be, all four, free from any trace of bifidity 
of the root. The upper bicuspids are larger than the lower ones, and their 
cups are more deeply divided. Sometimes the first lower bicuspid has only 




FORM OF PERMANENT TEETH. MOLARS. 783 

one tubercle distinctly marked, i. e., the external, and in that case approaches 
in figure to a canine tooth. 

The molar teeth, true or large molars, or multicuspid teeth, are twelve 
in number, and are arranged behind the bicuspid teeth, three on each 
side, above and below. They are distinguished by the large size of the 
crown, and by the great width of its grinding surface. The first molar 
is the largest, and the third is the smallest, in each range, so as to pro- 
duce a gradation of size in these teeth. The last molar in each range, 
owing to its late appearance through the gums, is called the wisdom- 
toothy dens sapientise. The crowns of the molar teeth are low and cuboid 
in their general form. Their outer and inner surfaces are convex, but 
the crowns are rather flattened before and behind. The grinding surface 
it nearly square in the lower teeth, and rhomboid al in the upper, the 
corners being rounded off : it is not smooth, but is provided with four or 
five trihedral tubercles or cusps (whence the name of multicuspidati), sepa- 
rated from each other by a crucial depression. The upper molars have 
four cusps situated at the angles of the masticating surface ; of these the 
internal and anterior cusp is the largest, and is frequently connected with 
the posterior external cusp by a low oblique ridge. In the upper wisdom- 
teeth, the two internal tubercles are usually blended together. The crowns 
of the lower molars, which are larger than those of the upper, have five 
cusps, the additional one being placed between the two posterior cusps, and 
rather to the outer side : this is especially evident in the lower wisdom- 
teeth, in which the crown is smaller and rounder than in the others. The 
fangs of all the molar teeth are multiple. In the two anterior molars of 
the upper jaw, they are three in number, viz. two placed externally, which 
are short, divergent, and turned towards the antrum of the superior max- 
illa ; and a third or internal fang, which is larger and longer, and is directed 
towards the palate, the posterior border of which extends as far back as that 
of the posterior external fang. This third fang is often slightly grooved, 
especially when the two internal cusps are very distinct, and sometimes it 
is divided into two smaller fangs. The two anterior molars of the lower 
jaw have each two fangs, one anterior, the other posterior, which are broad, 
compressed, and grooved on the faces that are turned towards each other, 
as if each consisted of two fangs fused together : they have an inclination 
or curve backwards in the jaw, and are slightly divergent, or sometimes 
parallel, or even nearly in contact with each other : more rarely one or both 
of them is divided into two smaller fangs. In the wisdom-teeth of both 
jaws the fangs are often collected into a single irregular conical mass, which 
is either directed backwards in the substance of the jaw, or curved irregu- 
larly : this composite fang sometimes shows traces of subdivision, and there 
are occasionally two fangs in the lower tooth and three in the upper. 

The bicuspid and the molar teeth, from the breadth and uneven form of 
their crowns, are fitted for bruising, crushing, and grinding the food in 
mastication. 

The range of teeth in each jaw forms a nearly uniform curve, which is 
not broken by any intervals, as is the case in the dental apparatus of many 
animals, even in the Quadrumana. The upper dental arch is rather wider 
than the lower one, so that the teeth of the upper jaw slightly overhang 
those of the lower. This is owing principally to the fact that the lower 
teeth are placed either vertically, as in front, or are inclined somewhat 
inwards, as is seen behind and at the sides, while the corresponding teeth 
of the upper jaw have an inclination forwards in front, and outwards 



784 



ORGANS OF DIGESTION. 



behind. While there is a slight diminution in the height of the exposed 
parts of the teeth from the incisors backwards to the wisdom-teeth, there is 
in man a general uniformity in the amount of projection of the crowns 
throughout the whole series. In consequence of the large proportionate 
breadth of the upper central incisors, the other teeth of the upper jaw are 
thrown somewhat outwards, so that in closure of the jaws the canine and 
bicuspid teeth come into contact partly with the corresponding lower teeth 
and partly with those next following ; and in the case of the molar teeth, 
each cusp of the upper lies behind the corresponding cusp of the lower 
teeth. Since, however, the upper wisdom-teeth are smaller than those 
below, the dental ranges terminate behind nearly at the same point in both 
jaws. 

The Milk-teeth. The temporary incisor and canine teeth resemble those of 
the permanent set in their general form ; but they are of smaller dimen- 
sions. The temporary molar teeth present some peculiarities. The hinder 
of the two is much the larger ; it is the largest of all the milk-teeth, and 
is larger even than the second permanent bicuspid, by which it is afterwards 
replaced. The crown of the first upper milk molar has only three cusps, 

Fig. 542. 





Fig. 542. MILK TEETH OP THE RIGHT SIDE OF THE UPPER AND LOWER JAWS. 
a, the incisors ; 6, the canines ; c, the molar teeth. 

two external and one internal ; that of the second has four distinct cusps. 
The first lower temporary molar has four cusps, and the second five, of which 
in the latter case three are external. The fangs of the temporary molars 
resemble those of the permanent set, but they are smaller, and are more 
divergent from the neck of the tooth. 

Structure. On making a section of a tooth, the hard substance of 
which it is composed is found to be hollow in the centre. The form of the 
cavity bears a general resemblance to that of the tooth itself : it occupies the 
interior of the crown, is widest opposite to or a little above the neck, and ex- 
tends down each fang, at the point of which it opens by a small orifice. In 
the crown of the incisor teeth the cavity is prolonged into two fine linear 
canals, which proceed one to each corner of the crown ; in the bicuspid and 
molar teeth it advances a short distance into each cusp. In the case of a root 
formed by the blending of two or more fangs, as occurs occasionally in the 
wisdom-teeth, each division has a separate canal prolonged down to its apex. 



STRUCTURE OF THE DENTINE. 



785 



The central cavity of a tooth is called the pulp-cavity, because it is occupied 
and accurately filled by a soft, highly vascular, and sensitive substance, 



Fig. 543. 




Fig. 543. SECTIONS OP AN INCISOR AND 
MOLAR TOOTH. 

The longitudinal sections show the whole 
of the pulp-cavity in the incisor and molar 
teeth, its extension upwards within the crown 
and its prolongation downwards into the fangs 
with the small aperture at the point of each ; 
these and the cross section show the relation 
of the dentine and enamel. 



called the dental pulp. This pulp con- 
sists of areolar filaments, amongst 

which numerous nuclei and cells are rendered visible by the action of acetic 
acid. It is well supplied with vessels and nerves, which are derived from 

Fig. 544. MAGNIFIED LONGITUDINAL SECTION OF A Fig. 544. 

BICUSPID TOOTH (after Ketzius). 

1, the ivory or dentine, showing the direction and pri- 
mary curves of the dental tubuli ; 2, the pulp-cavity with 
the small apertures of the tubuli into it ; 3, the cement or 
crusta petrosa covering the fang as high as the border of 
the enamel at the neck, exhibiting lacunae ; 4, the enamel 
resting on the dentine ; this has been worn away by use from 
the upper part. 

the internal maxillary artery and the fifth pair, and 
which enter the cavity through the small aperture 
at the point of each fang. 

The solid portion of the tooth is composed of 
three distinct substances, viz. the proper dental 
substance, ivory or dentine, the enamel, and the 
cement or crusta petrosa. The dentine constitutes 
by far the larger part of the hard substance of a 
tooth ; the enamel is found only upon the exposed 
part or crown ; and the cement covers with a thin 
layer the surface of the implanted portion or fang. 
A fourth variety of tissue, osteodentine, is formed 
within the dentine, at the expense of the pulp, as 
age advances. 

A. The dentine, (Owen,) forming the principal 
mass or foundation of the body and root of a tooth, 
gives to both of these parts their general form, 
and immediately encloses the central cavity. It 

resembles very compact bone in its general aspect and chemical relations, 
but is not identical with it in structure, or in the exact proportions of its 
earthy and animal constituents. 

According to the analyses of Berzelius and Bibra, the dentine of human 
teeth consists of 28 parts per cent, of animal, aud 72 of earthy matter. 
The former is resolvable into gelatin by boiling. The composition of the 
latter, according to Bibra, is as follows, viz. , phosphate of lime 66 '7 per cent., 
carbonate of lime 3 '3, phosphate of magnesia and other salts, including a 
trace of fluoride of calcium, ! 8. Berzelius found 5 *3 carbonate of lime. 

3 F 




786 



THE TEETH. 




Examined under the micro- 
scope, dentine is seen to consist 
of an immense number of very 
fine tubes, imbedded closely 
together in a hard intertubular 
matrix, and having the appear- 
ance of possessing distinct parie- 
tes. These dental tubules open 
at their inner ends into the pulp- 
cavity, the wall of which pre- 
sents very numerous minute ori- 
fices over the whole of its inner 
surface. Fruin thence they 
pass in a radiated manner 

Fig. 545. SECTIONS OP DENTINE 
(from Kolliker). 

A, highly magnified cross sections of 
the tubuli of dentine. f-. a, from 
a part in which the tubuli are very 
closely set ; b, from a part where 
they are widely set. 

B, longitudinal section of the root. 
2fQ a, the dental tubes near the inner 
surface of the dentine with few tubuli ; 
6, subdivision of tubuli ; c, looped 
disposition of the tubuli ; d, granular 
layer consisting of small dental glo- 
bules at the margin of the dentine ; 
e, lacunas of the cement, one of them 
connected by tubuli with those of the 
dentine. 

through every part of the ivory 
towards its periphery. In the 
upper portion of the crown they 
have a vertical direction ; but 
towards the sides, and in the 
neck and root, they become 
gradually oblique, then hori- 
zontal, and are finally even in- 
clined downwards towards the 
point of the fang. The course 
of the tubules is not straight, 
but each describes, in passing 
from the central to the peri- 
pheral part of the dentine, two 
or three gentle curves' (primary 
curvatures, Owen), and is be- 
sides bent throughout its whole 
length into numerous fine undu- 
lations, which follow closely one 
upon another ; these are the 
secondary curvatures. The cur- 
vatures of adjacent tubules so 



THE DENTAL TUBULES. 787 

far correspond, that the tubes are on the whole nearly parallel, being only 
slightly divergent as they pass towards the surface ; and as they divide 
several times dichotomously, and at first without being much diminished in 
size, they continue to occupy the substance of the dentine with nearly equi- 
distant tubes, and thus produce, when seen in fine sections of the tooth 
made parallel to their course, a striated appearance, as if the dentine were 
made up of fine parallel fibres. The concurrence of many of these parallel 
curvatures of the dental tubuli produces, by the manner in which they 
reflect the light, an appearance of concentric undulations in the dentine, 
which may be well seen with a low magnifying power. This, however, is 
not to be confounded with another set of curved marks called contour lines, 
which depend on conditions of the matrix, and will be afterwards described. 
The average diameter of each tubule near its inner and larger end is -j^^th 
of an inch, and the distance between adjacent tubules is about two or three 
times their width. (Retzius.) From their sides numerous immeasurably 
fine branches are given off, which penetrate the hard iutertubular substance, 
where they either anastomose or terminate blindly. These lateral ramuscles 
are said to be more abundant in the fang. Near the periphery of the ivory 
they are very numerous, and, together with the main tubules themselves, 
which there, by rapid division and subdivision, also become very fine, ter- 
minate by joining together in loops, or end in little dilatations, or in the 
cells of the granular layer to be described. 

The dental tubules, when highly magnified, appear like dark lines against 
transmitted light, but are white when seen upon a black ground. Their 
tubular character is proved by the fact that ink, or other coloured fluids, 
together with minute bells of air, can be made to pass along them, in sec- 
tions of dry teeth. Their walls, in transverse sections, may often appear 
thicker than they are in reality, owing to a certain length of the tubes being 
seen in the section : but if the orifice of the canal be brought exactly into 
focus, the wall appears as only a very thin, yellowish border ; and, indeed, 
Kolliker denies the existence of any wall distinct from the matrix. From 
the researches of Nasmyth, Tomes, and Kolliker, it appears that in the 
recent state the tubules are filled with substance (dental fibres), continuous 
with the pulp of the tooth : and it is suggested by Tomes that this is not 
only subservient to the nutrition of the dentine, but probably also confers 
on it a certain degree of sensibility. It has been noticed, indeed, that the 
dentine is more sensitive near the surface than deeper in its substance, a 
fact not easily intelligible on the supposition that the sentient tissue is 
confined to the pulp-cavity. 

In the temporary, and sometimes even in the permanent teeth, the tubules are 
constricted at short intervals, so as to present a moniliform character. The terminal 
branches of tubules are occasionally seen to pass on into the cement which covers the 
fang, and to communicate with the small ramified canals of the characteristic lacunas 
found in that osseous layer. Tubules have likewise been observed by Tomes passing 
on into the enamel, more especially in the teeth of marsupial animals, but in a less 
marked degree in human teeth. 

The intertubular substance is translucent. The animal matter which 
remains in it, after the earthy matter has been removed by an acid, 
exhibits a tendency to tear in the direction of the tubules, but is in reality 
a homogeneous substance, deposited in a laminated manner. This was 
shown by Sharpey, who observed that in the softened teeth of the cachalot 
or sperm-whale the animal substance was readily torn into fine lamellae, 
disposed parallelly with the internal surface of the pulp-cavity, and there- 

* 3 F 2 



788 



THE TEETH. 



fore across the direction of the tubules. In these lamellse the sections of 
the tubules appeared as round or oval apertures, the lamellae having the 
same relation to the tubules as those of true bone to the canaliculi. The 
same tendency to lamination may be exhibited by boiling a longitudinal 
section of tooth with caustic potash, after which it presents closely set, short, 
and regular fissures, lying at right angles to the tubules, throughout the 
extent of the dentine. (Cleland.) 

Fu. 546. 






~e 



Fig. 546. VERTICAL SECTION OP THE UPPER 
PART OF AN INCISOR TOOTH (from Kol- 
liker). f 

a, the pulp-cavity ; b, dentine or tubular 
substance ; c, arched contour lines with inter- 
globular spaces ; d, cement ; e, cuamel with 
an indication of the direction of the columns ; 
/, coloured lines of the enamel. 



Fig. 547. A SMALL PORTION OP THE DENTINE 
WITH INTEHGLOBULAR SPACES (from K61- 
liker). 3 f 

6, the tubules ; c, the interglobular spaces 
filled with air. 



A laminated structure of a more distinct description has been observed 
in the dentine of the crown, giving rise to the appearances in longitudinal 
sections termed contour lines. Czermak states that transverse sections of 
the tooth present concentric lines resembling the year-rings of wood : and 
Salter has shown that decalcified specimens readily break up in these lines ; 
the crowns of the teeth consisting of a series of superimposed hollow 
cones : the intervals between their strata, in longitudinal sections, appearing 
as contour markings, in transverse sections as annular lines ; in both cases 
corresponding with the surface of the pulp, as it existed during the forma- 
tion of the tooth. The contour markings, when examined with the micro- 
scope, are seen to be caused by irregularities of the intertubular tissue, 
which, opposite these marks, presents the appearance of spaces or clefts 
bounded by globular masses of the ordinary tubular and dense substance. 
These globules vary in size from -^oth to TQ^TTO^ f an * ncn 5 tne largest 
being in the crown, the smallest in the fang. The tubuli pass through these 
globules, and appear to be continuous in direction across the interspaces 
from one globule to another. 



STRUCTURE OF THE EXAMEL, 



789 



Another kind of irregularity in the structure of the dentine gives rise to 
the granular layer of Purkinje ; the peculiarity of which consists in the 
presence of a number of minute cell-like cavities, which break up the 
uniformity of the matrix, and by branches anastomose one with another 
and receive terminations of dental tubuli. They are found principally in 
a layer beneath the cement, and also beneath the enamel. The circum- 
stance of their forming connections with the tubules points to a difference 
in nature between these cavities and the much larger iuterglobular spaces. 

The surface of the dentine where it is in con- 
tact with the enamel is marked by undulating 
grooves and ridges, and also by numerous minute 
hexagonal depressions, to which the microscopic 
fibres of the enamel are accurately adapted. 

B. The enamel is that hard white covering 
which encrusts and protects the exposed portion 
or crown of a tooth. It is the hardest of all the 
dental tissues, but it is gradually worn down by 
protracted use. It is thickest on the grinding 
surface and cutting edges of the teeth, and be- 
comes gradually thinner towards the neck, where 
it ceases. Its extent and thickness are readily 

Fig. 548. THIN SECTION OF THE ENAMEL AND A PART 
OF THE DENTINE (from Kb'lliker). r f 

a, cuticular pellicle of the enamel ; 6, enamel-fibres or 
columns with fissures between them and cross striae ; c, 
larger cavities in the enamel communicating with the 
extremities of some of the tubuli (d). 

seen on charring the tooth, by which the dentine 

becomes blackened, whilst the enamel, owing to 

the very small quantity of animal matter in its 

composition, remains white. According to Bibra 

it contains of earthy constituents 96 '5 per cent., 

viz. phosphate of lime with traces of fluoride of 

calcium 89 '8, carbonate of lime 4 -4, phosphate 

of magnesia and other salts 1'3 ; and has only 

3-5 per cent, of animal matter. Berzelius, however, gives the proportion 

of carbonate of lime as 8, and of animal matter as only 2 per cent. 

The enamel is made up entirely of very hard and dense microscopic fibres 
or prisms, composed almost wholly of earthy matter, arranged closely to- 
gether, side by side, and set by one extremity upon the subjacent surface of 
the dentine. On the summit of the coronal portion of the tooth these 
enamel fibres are directed vertically, but on the sides they are nearly hori- 
zontal. As seen in a section they are disposed in gently waving lines, 
parallel with each other, but not so regular as the curvatures of the tubuli 
of the dentine, with which they have no agreement. The concurrence of 
these parallel curvatures produces, as in the case of the dentine, an appear- 
ance of concentric undulations in the enamel, which may be seen with a 
lens of low power. A series of concentric lines is likewise to be seen 
crossing the enamel fibres, as the contour lines cross the dentine : these are 
termed coloured lines from their brown appearance, but they seem rather to 
depend on lamination than on pigmentary deposit. Minute fissures not 
unfrequently exist in the deep part of the enamel, which run between 




790 



THE TEETH. 



clusters of the fibres down to the surface of the dentine ; and other much 
larger and more evident fissures are often observed leading down from the 
depressions or crevices between the cusps of the molar and premolar teeth. 
The surface of the enamel, especially in the milk-teeth, is marked by 
transverse ridges, which may be distinguished with a common magnifying 
glass. 

Fig. 549. 




Fig. 549. ENAMEL FIBRES (from Kolliker). s f 

A, fragments and single fibres of the enamel, isolated by the action of hydrochloric acid. 

B, surface of a small fragment of enamel, showing the hexagonal ends of the fibres. 

The enamel-fibres have the form of solid hexagonal prisms. Their dia- 
meter varies slightly, and is ordinarily about j^o^th of an inch. They are 
marked at small intervals by dark transverse lines. According to Tomes, 
the fibre is not in all cases solid, but has occasionally an extremely minute 
cavity in part or in the whole of its length, which is best seen in newly- 
developed enamel, but is also visible in adult teeth. The inner ends of the 
prisms are implanted, as it were, into the minute hexagonal depressions 
found on the surface of the dentine, whilst the outer ends, somewhat larger 
in diameter, are free, and present, when examined with a high magnifying 
power, a tesselated appearance. 

When submitted to the action of dilute acids, the enamel is almost 
entirely dissolved, and leaves scarcely any discernible traces of animal 
matter. Near the deep surface this is rather more abundant, according to 
the observations of Retains, who conceived that it there aided in fixing the 
enamel fibres. By the action of an acid, the enamel of newly formed or 
still growing teeth may be broken up, and its structural elements more 
easily distinguished. The prisms are then found to have interposed between 
them a delicate membranous structure, forming sheaths in which the cal- 
careous matter is deposited. As this latter accumulates, the membranous 
structure becomes almost or entirely obliterated, and the now earthy prisms 
are inseparably consolidated. Each membranous sheath, according to Tomes, 
contains a line of granular cells or masses, arranged in single series like the 
sarcous elements in muscular fibres, and thus occasioning the transverse 
markings. 



STRUCTURE OF THE CEMENT. 



791 



It is also found, on treatment with acid, that a very thin membrane 
called by Kolliker "cuticle of the enamel," and by Busk and Huxley 
" Nasmyth's membrane, " (after its discoverer), entirely covers the enamel upon 
its outer surface. This membrane, which is calcined in the natural state, 
forms a protective covering to the enamel. Berzelius and Retzius say that 
a similar membrane also exists between the enamel and the dentine, but 
Kolliker has been unable to find any in that situation. 

c. The crusta petrosa or cement is the third substance which enters into 
the formation of the teeth. This is a layer of true bone, slightly modified 
in structure, and investing that part of the dentine which is not protected 
by the enamel. It covers the whole fang, towards the lower end of which 
it becomes gradually thicker, and is especially developed at the apex, and 
along the grooves of the compound fangs. Besides this, the calcified mem- 
brane or cuticle on the surface of the enamel has been regarded by various 
writers as a coating of cement iu that situation, the representative of the 
coronal cement on the compound teeth of many herbivorous animals. As 
life advances, the cement generally becomes thicker, especially near the 
apex of the fang, where it sometimes blocks up the orifice leading into the 
pulp-cavity. 

The crusta petrosa contains cells and canaliculi resembling those of bone ; 
they are placed lengthwise around the fang, and give off minute radiated 
ramifications, which are often found to proceed from one side only of a cell, 
towards the periodontal surface (Tomes). In the deeper layers of the 
cement the fine canaliculi sometimes anastomose with some of the terminal 
tubules of the subjacent dentine. Where the cement is very thick it may 
contain vascular canals, analogous to the Haversian canals of bone. On the 
deciduous teeth the cement is thinner, and contains fewer cells. It has been 
shown by Sharpey that perforating fibres, similar to those of ordinary bone, 
run abundantly through the cement. In chemical composition it resembles 
bone, and contains 30 per cent, of animal matter. The cement is, according 
to some, extremely sensitive at the neck of the tooth, if it be exposed by 




Fig. 550. SECTION OP A PORTION OP THE DENTINE AND CKMENT FROM THE MIDDLE OF 
THE ROOT OP AN INCISOR TOOTH (from Kolliker). 3 f 

a, dental tubuli ramifying and terminating, some of them in the interglobular spaces 
(b and c), which resemble somewhat bone-laeunse ; d, inner layer of the cement witl\ 
numerous closely set canaliculi ; e, outer layer of cement; /, lacunce ; y, canaliculi. 



792 THE TEETH. 

retraction of the gum. By its connection with the surrounding mem- 
branous structures it contributes to fix the tooth in the socket. It is the 
seat of the bony growths or exostoses sometimes found upon the teeth. 

D. Osteodentine (Owen), secondary dentine (Tomes), or the horny substance 
of Blumenbach, is a hard substance which begins to be deposited on the 
inner surface of the dentine after the age of twenty years or later, so that 
the central cavity of a tooth becomes gradually diminished in size, whilst 
the pulp slowly shrinks or disappears. This additional substance, formerly 
regarded as an extension of the cement into the interior of the tooth, has 
been shown to have a distinct structure, in part resembling dentine, and in 
part bone. It is traversed by canals, which contain blood-vessels, and are 
surrounded by concentric lamellae, like the Haversian canals of bone. From 
these canals, numerous tubules radiate in all directions, larger than the 
canaliculi of bone, resembling, in this respect, and also in their mode of 
ramification, the tubes of the dentine. This newly added structure may or 
may not coalesce with the previously formed dentine ; it appears to be pro- 
duced by a slow conversion of the dental pulp. 

Among special works on the teeth may be noticed, Retzius, in Muller's Archiv, 
1837; Nasmytk, Researches on the Teeth, 1839; Owen, Odontography, 1840-45; 
Tomes, Lectures on Dental Physiology and Surgery, 1848, also in the Phil. 
Transactions, 1849 and 1850, and in Quart. Journ. of Micr. Science, 1856; Salter, 
in Quarterly Journal of Microscopic Science, 1853, in Guy's Hospital Reports, third 
series, vol. i. ; and in Trans. Path. Soc., 1854 and 1855 ; Czermak in Zeitschrift fur 
wissensch. Zoologie, 1850; Huxley in Quarterly Journal of Microscopic Science, 1853. 

DEVELOPMENT OP THE TEETH. 

Although the general phenomena of the growth and succession of the 
teeth had received considerable attention from various anatomists, the ob- 
servations of Arnold and Goodsir, made independently of each other, more 
especially the latter, were the first to give precision to our knowledge 
concerning their origin and the earlier stages of their formation. More 
recent researches have, it is true, shown that their account of the primor- 
dial condition of the dental germs may require some modification ; but 
nevertheless these authors were the first to establish the primordial con- 
nection of the teeth with the mucous membrane covering the edges of the 
maxillary arches, and Goodsir was the first to give a consistent view of the 
earlier steps of the formative process in the temporary and permanent series 
of teeth. (Arnold in Salzbtirger Med. Zeitung, 1831 ; Goodsir in Edin. 
Med. and Surg. Journal, 1839.) The changes which take place in the 
bones of the jaws relate only to the formation of the sockets of the teeth. 
In their earliest condition these bones present no appearance of alveoli, 
but, concurrently with certain changes in the mucous membrane, to be 
immediately described, a wide groove is developed aloi.'g the edge of the jaw, 
which gradually becomes deeper, and is at length divided across by thin 
bony partitions, so as to form a series of four-sided cells. These bony septa 
are not distinctly formed until near the fifth month of foetal life. By the 
subsequent growth of the bone, these cavities or loculi are gradually closed 
round, except where they remain open at the edge of the jaw. By the end 
of the sixth month they are distinctly formed, but continue afterwards, in 
proportion to the growth of the teeth, to increase in size and depth, by the 
addition of new matter which widens and deepens the jaw. 

The first stages in the development of the teeth, as observed by Arnold 
and Goodsir, consist of certain changes in the mucous membrane cover- 



DEVELOPMENT OF THE TEETH. 793 

ing the borders of the maxilloe. About the sixth week of embryonic life, 
a depression or groove, having the form of a horse- shoe, appears along 
the edge of the jaw, in the mucous membrane of the gum ; this is the 
primitive dental groove (Goodsir), From the floor of this groove (supposed 
to be represented in a transverse section, in the diagrammatic figure 551,1) 

Fig. 551. 



/IS 1 





Fig. 551. DIAGRAMMATIC OUTLINES OP SECTIONS THROUGH THE DENTAL GERMS AND 
SACS, AT DIFFERENT STAGES OF DEVELOPMENT (from Goodsir). 

1, the primitive dental groove of the gum cut across in a foetus of about six weeks; 2, 
a papilla rising within the dental groove ; 3, 4, and 5, represent the follicular stage in 
which the papilla (or future tooth-pulp) is seen sunk within the follicle, and the lips of 
the follicle or opercula advancing towards each other gradually meet and close in the ful- 
licle; 5, may be looked upon as representing the section indicated by the line a b, in fig. 
559, through the sac of an incisor tooth, in which a lunated depression (c) is left behind; 
in 6, the lips of the groove are seen to come together ; in 7, the union of the lips being 
complete, the follicle becomes a closed sac s, containing the dental pulp p, and having 
behind it the lunated depression c, now also enclosed, and forming the cavity of reserve 
for the germ of the corresponding permanent tooth ; in the remaining outlines, 8 to 12, 
are shown the commencement of the cap of dentine on the pulp, the subsequent steps in 
the formation of the milk tooth, and its eruption through the gum (11); also the gradual 
changes in the cavity of reserve, the appearance of its laminae and papilla, its closure to 
form the sac of the permanent tooth, its descent into the jaw, behind and below the milk 
tooth, and the long pedicle (12) formed by its upper obliterated portion. 

a series of ten papillae, as at 2, arise in succession in each jaw, and consti- 
tute the germs or rudimentary pulps of the milk-teeth. These pulps or 
papillae are processes of the mucous membrane itself, and not mere eleva- 
tions of its epithelium. The order in which they appear is very regular. 
The earliest is that for the first milk molar tooth : it is seen at the seventh 
week, as soon as the dental groove is formed ; at the eighth week that for 
the canine tooth appears ; the two incisor papillae follow next, at about the 
ninth week, the central one before the lateral ; lastly, the second molar 
papilla is visible at the tenth week, at which period this, the papillary stage 
of the rudiments of the teeth is completed. The papillae in the upper jaw 
appear a little earlier than those in the lower jaw. In the next place, the 
margins of the dental groove become thickened and prominent, especially 
the inner one ; and membranous septa or prolongations of the mucous mem- 
brane pass across between the papillae from one margin to the other, so as 
to convert the bottom of the groove into a series of follicles, each containing 
one of the papillae. These changes constitute the follicular stage ; they take 
place in the same order as that in which the papillae make their appearance, 
and are completed about the fourteenth week. During the early part of this 



794 THE TEETH. 

period the papillce grow rapidly, they begin to show peculiarities of form, and 
project from the mouths of the follicles. Soon, however, the follicles become 
deeper, so as to hide the papillae, which now assume a shape corresponding 
with that of the crowns of the future teeth. Small laminae or opercula of 
membrane are then developed from the sides of each follicle, their number 
and position being regulated, it is said, by the form of the cutting edges 
and tubercles of the coming teeth : the incisor follicles having two laminae, 
one external and one internal ; the canine, three, of which two are internal ; 
and the molars, four or five each. The lips of the dental groove, as well as 
the opercula, now begin to cohere over the follicles from behind forwards, 
the posterior lip being very much thickened ; the groove itself ia thus 

Fig. 552. Fig. 552. ENLARGED VIEW OP THE UPPER AND 

LOWER DENT\L ARCHES OP A FCETUS OP ABOUT 
FOURTEEN WEEKS. 

This specimen shows the follicular stage of develop- 
ment of all the milk teeth as described by Goodsir ; 
in each follicle the papilla is seen projecting ; but this 
exposure of the papillae and the cavity of the follicles 
probably arises from the accidental loss of the epithe- 
lial covering. 

gradually obliterated, the follicles are con- 
verted into close sacs, and the saccular stage 
of the milk-teeth is thus completed about the 
end of the fifteenth week. Certain lunated 
depressions, which are formed one behind each 
of the milk -follicles about the fourteenth week, 
escape the general adhesion of the lips of the 

groove. From these depressions, as will b'e afterwards described, the sacs 
of the ten anterior permanent teeth are subsequently developed. 

The first stages in the development of the teeth here described, the superficial origin 
and open condition of the dental sacs, and the free papillary commencement of the 
pulps, have been denied in recent years by Guillot, and by Robin and Magitot, who 
assert that the sacs with their contents make their first appearance in the submucous 
tissue, and are from the first closed sacs (Guillot in Annales des Sciences Naturelles, 
vol. ix., 1859; Robin and Magitot in Journal de la Physiologic, 1860, vol. iii., pp. 
130 and 663). The observations of Kolliker, however, seem to furnish a clue to the 
explanation of what has been seen by these authors, at the same time that they con- 
firm, in its most important features, Goodsir's mode of viewing the phenomena. In 
the foetal lamb and calf, the first step in the formation of the tooth-germ, observed by 
Kolliker, consists in a depression of a part of the deepest layer of the epithelium 
into the subjacent mucous membrane. This depression, which, in common with 
Huxley, he regards as the commencement of the foetal structure known as the enamel 
organ, to be afterwards described, widens subsequently, so as to become flask-shaped, 
remaining connected with the deep surface of the epithelium by a narrow neck. In 
the next stage the dental papilla rising from the surface of the mucous membrane, 
projects into, or indents the deepest side of the epithelial process or future enamel 
organ, and the dental sac is formed at a somewhat later period in the surrounding 
substance of the mucous membrane. In these animals, therefore, the epithelium of 
the edge of the jaw covers in completely the enamel-germ or primary tooth-follicle. 

In man, Kolliker was unable to discover a similar arrangement, but found matters 
very much, in the disposition described by Goodsir; that is, the follicles open, situated 
in a dental groove of the jaw, and containing at their deepest part the dental papilke 
developed from the mucous membrane. But he conceives it not improbable that in 
Goodsir's specimens, as well aa in his own, the whole of the epithelium had been 
abraded, and that the follicles and papillae were thus unnaturally opened to the surface. 




ORIGIN OF THE DENTAL GERMS. 



795 



Fig. 553. DIAGRAMS OF THE MODE OP 
ORIGIN OF THR DENTAL GEKM IN 
THE RUMINANT (after Kolliker). 

The three figures represent trans- 
Terse sections of the gum and a part of 
the jaw at or shortly after the period 
of the formation of the germ, and are 
designed chiefly to show the relation of 
the germ to the epithelium. 

A, represents the state in a very 
early condition, when the primitive 
deutal follicle of a milk or temporary 
tooth has been formed by a depression 
from the deep layer of the epithe- 
lium. 

B, represents a later stage, when the 
tooth-papilla has risen from the surface 
of the mucous membrane, and has 
inflected the primitive dental follicle. 

C, represents a more advanced stage 
in which the dental sac has begun to 
be formed. 

c, the superficial thick epithelium of 
the gum only sketched in outline ; c', 
the deep layer of cylindrical cells ; /, 
the primitive tooth -follicle ; /', its cel- 
lular or granular contents and cavity ; 
p, the dental papilla, and afterwards 
tooth-pulp ; e, the inner inflected layer 
of the wall of the primitive follicle 
forming the inner part of the enamel 
organ ; e', the outer wall of the same 
with the epithelial sprouts shooting into 
the tissue above ; s, the commencement 
of the dental sac ; fp, the follicle of 
the corresponding permanent tooth. 

Waldeyer has shown by more 
recent observations, that in the 
human embryo the teeth arise in a 
manner essentially the same as that 
described by Kolliker in the rumi- 
nant. (Waldeyer, lib. die Entwick. 
<ler ZShne, Zeitsch. fur. ration. Me- 
dicin, 1865, and Henle's Bericht, &c. 
for 1864, p. 81.) 

The dental sacs, after the 
closure of the follicles, continue 
to enlarge, as do also their con- 
tained papillae. The walls of 
the sacs, which soon begin to 
thicken, consist of an outer tibro- 
areolar membrane, and an in- 
ternal highly vascular layer, 
lined by epithelium ; their blood- 
vessels are derived partly from 
the dental arteries which course 
along the base of the sacs, and 
partly from those of the gums. 

The papillse, now the dental 
pulps, acquire a perfect resem- 



Fig. 553. 









796 THE TEETH. 

blance to the crowns of the future teeth, and then the formation of the 
hard substance commences in them. This process begins very early, and by 
the end of the fourth month of foetal life thin shells or caps of dentine are 
found on all the pulps of the milk-teeth, and a little later on that of the 
first permanent molar, while at the same time the coating of enamel begins 
to be deposited on each. The cap of dentine increases in extent by a growth 
around its edges, and in thickness by additions in its interior, at the expense 
of the substance of the pulp itself, which decreases in proportion. Thia 
growth of the tooth continues until the crown is completed of its proper 
width, and then the pulp undergoes a constriction at its base to form the 
cervix of the tooth, and afterwards elongates and becomes narrower, so as to 
serve as the basis of the fang. Sooner or later, after the completion of the 
crown, this part of the tooth appears through the gum, whilst the growth of 
dentine to complete the fang is continued at the surface of the elongating 
pulp, which gradually becomes encroached upon by successive formations of 
hard substance, until only a small cavity is left in the centre of the tooth, 
containing nothing but the reduced pulp, supplied by slender threads of 
vessels and nerves, which enter by a small aperture left at the point of the 
fang after the dentine is completed. In the case of teeth having complex 
crowns and more than a single fang, the process is somewhat modified. On 
the surface of the dental pulp of such a tooth, as many separate caps or 
shells of dental substance are formed as there are eminences or points ; these 
soon coalesce, and the formation of the tooth proceeds as before as far as the 
cervix. The pulp then becomes divided into two or more portions, corres- 
ponding with the future fangs, and the ossification advances in each as it 
does in a single fang. A horizontal projection or bridge of dentine shoots 
across the base of the pulp, between the commencing fangs, so that if the 
tooth be removed at this stage and examined on its under surface, its shell 
presents as many apertures as there are separate fangs. In alt teeth, the 
pulp originally adheres by its entire base to the bottom of the sac ; but, when 
more than one fang is to be developed, the pulp is, as it were, separated 
from the sac in certain parts, so that it comes to adhere at two or three in- 
sulated points only, whilst the dentine continues to be formed along the 
intermediate and surrounding free surface of the pulp. 

Formation of the hard tissues of the teeth. Previously to the commencement of 
ossification, the primitive pulp is found to consist of microscopic nucleated cells 
(pulp-granules, Purkinje), more or less rounded in form, and imbedded in a clear 




Fig. 554. DIFFERENT STAGES IN TTTE FORMATION OF A MOLAR TOOTH WITH Two 

FANGS (from Blake). 

1, the distinct caps of dentine for five crowns in the earliest stage of formation ; in 2, 
and the remaining figures, the crown is downwards ; in 2 and 3, the formation of the 
crown having proceeded as far as the neck, a bridge of dentine stretches across the base 
of the tooth-pulp ; and in 4, the division of the fangs is thus completed ; in 5, 6, and 7, 
the extension takes place in the fangs. 



FORMATION OF THE DEXTAL SUBSTANCES. 



797 



matrix containing a few very fine molecules, thinly disseminated in it. At the 
exterior of the pulp, the cells become elongated, and arranged perpendicularly to the 

Fig. 555. VERTICAL TRANSVERSE SEC- Pig 555^ 

TION OF THE DENTAL SAC, PULP, &C. , 

OF A KITTEN (from Kolliker after a 
preparation by Tiersch). \* 

a, dental papilla or pulp, the outer 
darker part consisting of the dentine 
cells ; 6, the cap of dentine formed upon 
the summit ; c, its covering of enamel ; 
d, inner layer of epithelium of the 
enamel organ ; e, gelatinous tissue ; /, 
outer epithelial layer of the enamel 
organ ; g, inner layer, and h, outer 
layer of the dental sac. 

surface, so as to form a tolerably regular 
layer, resembling a columnar epi- 
thelium. The pulp contains white 
areolar fibres, without any elastic or 
yellow tissue, and it is highly vascular. 
The capillary vessels are most abun- 
dant at the points where ossification 
is to commence ; they form a series of 
loops between rows of cells arranged 
in a radiate manner, but they do not 
reach the surface. Besides this, the 
entire pulp is covered by a fine pellucid 
homogeneous membrane, named the 
preformative membrane (Purkinje, 
Raschkow), or basement membrane. 
The space between the pulp and the 

wall of the sac is occupied by a delicate substance accurately applied to its surface. 
This is the outer pulp of Hunter, termed also the enamel-organ (organon adamantines, 
Purkinje), being generally considered to be connected with the formation of the enamel. 
It presents three layers ; viz., externally, an epithelial layer with prominences which 
fit in between vascular processes of the surrounding mucous membrane ; internally, a 
layer of cylindrical nucleated cells, named the enamel-membrane, resting on the pre- 
formative membrane ; and between these, a bulky substance, consisting of small stellate 
cells anastomosing by long processes, and having the large meshes between them filled 
with clear fluid. This structure was formerly supposed to be similar to the primitive 
pulp ; but, as was first stated by Huxley and since confirmed by Kolliker, the whole 
enamel-organ is epithelial in nature, being derived by invagination from the cuticle. 

The dentine is formed at the surface of the pulp, beneath the preformative mem- 
brane, but the precise manner in which it is derived from the soft tissues is still 
a matter for investigation, According to Purkinje, Retzius, and Raschkow, the 
preformative membrane is the part which first undergoes calcification, and after- 
wards the tissue of the pulp immediately beneath it. On gently separating the 
newly formed cap of dentine from the formative pulp, in the growing teeth of the 
human subject or of animals, and examining it under the microscope, the elongated 
cells of the pulp are found adhering in numbers to the inner surface of the newly- 
formed dentine. Owen states that the nuclei of the elongated cells, having them- 
selves become lengthened, divide both longitudinally and transversely to develop 
secondary cells which continue included within the primary cells. The secondary 
cells then elongate, and together with their nuclei join end to end. Calcification 
proceeds in all parts, except in the nuclei of the secondary cells which remain as 
the cavities or lumina of the tubes ; the walls of the secondary cells are supposed 
to form the parietes of the tubes, and the material between the secondary cells 
together with the walls of the primary cells to be converted into the intertubular sub- 
stance. The bifurcation of the tubuli is said to result from the junction of two 




798 



THE TEETH. 



secondary cells with a single one in a deeper layer of the pulp ; and the constricted or 
moniliform appearance of the tubuli already mentioned as having been seen by some 
observers in growing or even in mature teeth, is thought to depend on an imperfect 

Fig. 556. 




Fig. 556. VERTICAL SECTION THROUGH THE POINT OF A HUMAN FOETAL MILK TOOTH, IN 

WHICH THE FORMATION OF THE DENTINE AND ENAMEL HAS RECENTLY COMMENCED (from 

Kolliker after Lent). ^ 

a, dental pulp with blood-vessels ; 5, the dentine-cells upon its surface ; c, the cap of 
dentine which has been formed on the summit, the tubuli being shown as prolongations 
from the tapering extremities of the dentine-cells ; d, the enamel begun to be deposited ; 
c, membranous layer, mernbrana prseformativa of Huxley. 

coalescence of the nuclei. In the teeth of young animals, Tomes has noticed the 
division of the cells and their subsequent coalescence to form the tubes, but he has 
failed to recognise the existence of primary cells including secondary ones. Lent 
finds that the superficial elongated cells of the dentinal pulp send off from their 
free ends long slender processes which form the tubes of the dentine, and which divide 
into branches, and anastomose together in the same manner as the tubes. Kolliker, 
who confirms Lent's observations, thinks it probable that a single cell may generate a 
tube in its whole length ; at the same time a cell is sometimes constricted or incom- 
pletely divided into two, the more superficial of which becomes narrowed and length- 
ened into the dentinal tube. 

With respect to the actual formation of the hard substance of the tooth, two views 
have been entertained ; Kolliker conceiving it to proceed from the calcification of a 
soft matrix excreted from the dentinal cells and their thin prolongations already 
referred to ; whereas Waldeyer, who denies the existence of a preformative mem- 
brane, maintains that the formation of the dentine consists in the conversion of a part 
of the protoplasm of the dentinal cells into a collagenous substance, which is subse- 
quently calcified, while the remaining part of the cell-protoplasm continues in the 
form of soft fibres to occupy the interior of the tube surrounded by the calcified sub- 
stance. (Op. cit. p. 189.) When the cap of dentine is examined in the newly formed 
state, besides the ordinary dentine, globules are commonly observed ; but, if diluted 
hydrochloric acid be added, the globules disappear. Hence Czermak concludes that 
earthy impregnation proceeds for a time in a globular form, and that the after- 
presence of globular dentine is the result of arrested development; perfect develop- 
ment leading to the filling up of the spaces between the globules, and to the pro- 
duction of an uniformly compact tissue. 

The enamel appears in the form of prismatic fibres which, until the point was con- 
tested by Huxley, have been generally supposed to be produced by calcification of the 
cells of the enamel-membrane, with which they correspond in figure. An enamel 
fibre may be formed by a single cell growing in length, while its previously formed 



FORMATION OF THE ENAMEL. 



799 



Fig. 557. 



portion becomes calcified, or by the union of a series of successively formed cells 
arranged vertically to the surface. During its formation the enamel is soft and 
chalky, and can easily be separated into its com- 
ponent prisms. Afterwards the membranous por- 
tion of it is nearly all obliterated, and the nuclei 
entirely disappear, or, according to Tomes, elongate 

Fig. 557. A SECTION THROUGH THE ENAMEL ORGAN 
AND DENTAL SAC FROM THE TOOTH OP A CHILD AT 
BIRTH (from Kolliker). sp 

a, outer dense layer of the dental sac ; 6, inner 
looser texture of the same with capillary blood-vessels 
and a somewhat denser layer towards the enamel 
organ ; c, spongy substance ; d, inner cells ; and 
e, outer cellular layer of the enamel-organ. 

B, four cells of the enamel-membrane. S f2 

into a very fine central canal in each fibre. It is 
observed by Huxley that, if the pulp be treated 
with acetic acid, a voluminous, transparent mem- 
brane is raised from the whole surface in large folds, 
and that the ends of the enamel fibres are to be 
seen beneath it. The membrane is from -reV-a^h 
to -r^jth of an inch in thickness ; is clear, trans- 
parent, and exhibits little ridges bounding oval or 
quadrangular spaces ; and is, according to him, 
continuous with the membrana praeformativa. 
Huxley, therefore, considers that the enamel appears 
between the dentine and the preformative mem- 
brane, and that the enamel-organ takes no part 
in its formation. Tomes confirms the observation 
of Huxley with regard to the separability of this 
apparent membrane by acetic acid ; but, upon 
closer examination, finds that it may be split into 
columns, which are, in conformity with his view of 
the structure of enamel, sheaths containing nuclei. 
Tomes, further, believes that these sheaths may be 
seen to pass through the membrane, which Huxley 
describes as limiting them superficially ; and that, 
consequently, it is not, as Huxley imagines, the 
membrana praeformativa. "Waldeyer holds that the 
membrane described by Huxley between the 
enamel and the enamel-organ is only a layer of the 
most recently formed enamel, as he finds it pos- 
sible always to detect enamel-cells with the ends 
partially calcified. He returns, therefore, to 
Schwann's original view, that the formation of the 
enamel-columns is due to the direct calcification of 
the enamel-cell?* (Henle's Bericht, &c. for 1864, 
p. 81, and op. cit.) 

The Cement appears to be formed simultaneously 
with the dentine of the fang by the periodontal 
membrane. 

Eruption of the temporary teeth. At the 
time of birth the crowns of the anterior milk- 
teeth, still enclosed in their sacs, are com- 
pleted within the jaw, and their fangs begin 

to be formed. Their appearance through the gums follows a regular order, 
but the period at which each pair of teeth is cut varies within certain 





800 



THE TEETH. 



limits. The eruption commences at the age of eeven months, and is com- 
pleted about the end of the second year. It begins with the central incisors 



Fig. 558. 




Fig. 558. THE DENTAL 
SACS EXPOSED IN THE JAW 
OF A CHILD AT BIRTH. 

a, the left half seen from 
the inner side ; b, the right 
half seen from the outer 
side ; part of the hone has 
been removed so as to ex- 
pose the dental sacs as they 
lie below the gum ; the 
lower figure shows the sacs 
of the milk-teeth and the 
first permanent molar, ex- 
posed by removing the bone 
from the outside ; the upper 
figure shows the same from 
the inside, together with the 
pediculated sacs of the per- 
manent incisor and canine 
teeth adhering to the gum. 



of the lower jaw, which 
are immediately followed 

by those of the upper jaw ; and, as a general rule, each of the lower range of 

teeth rises through the gum before the corresponding tooth of the upper set. 

The following scheme indicates, in months, the order and time of eruption of 

the milk-teeth. 




MOLARS. 



CANINES. 



INCISORS. 



CANINES. 



24 12 


18 


9779 


18 


12 24 



Before the teeth protrude through the gum, this undergoes some peculiar 
changes : its edge at first becomes dense and sharp, but, as the tooth ap- 
proaches it, the sharp edge disappears, the gum becomes rounded or tumid, 
and is of a purplish hue ; the summit of the tooth is seen like a white spot 
or line through the vascular gum, and soon afterwards rises through it. As 
the crown of the tooth advances to its ultimate position, the elongated fang 
becomes surrounded by a bony socket or alveolus. Before the eruption, the 
mucous membrane is studded with a number of small white bodies, which 
were described by Serres as glands (dental glands), and were supposed by him 
to secrete the tartar of the teeth. Meckel thought they were small abscesses, 
because no aperture could be detected in them. In a fcetus of six months, 
they were found by Sharpey to be small round pearl- like bodies situated hi 
the corium of the mucous membrane, and having no aperture : they con- 
sist of small spherical capsules of various sizes, lined with a thick stratum 
of epithelium, the inner cells of which are flattened or scaly, like those lining 
the cheek, and are so numerous as almost to fill up the cavity. They are 
the prominences of the outer epithelial layer of the enamel organ, already 
referred to. 

Development of the permanent teeth. The preceding description of the 
structure of the dental sacs and pulps and of the mode of formation of the 




DEVELOPMENT OF THE PERMANENT TEETH. 801 

several parts of a tooth, applies to the permanent as well as to the milk- 
teeth. 

The origin and progressive development of the sacs of the permanent teeth 
have still to be considered. There are six more permanent teeth in each jaw 
than there are milk-teeth, and it is found that the sacs of the ten anterior 
permanent teeth, which succeed the ten milk-teeth, have a different mode of 
origin from the six additional or superadded teeth, which are formed further 
back in the jaw. 

Fig. 559. ENLARGED DIAGRAM OP THE DENTAL Fig. 559. 

ARCH ON THE LEFT SIDE ov THE LOWER JAW OF A 

FCETUS OF ABOUT FOURTEEN WEEKS (slightly 

altered from Goodsir). 

/, the follicles of the five milk-teeth, supposed lo 
be open, showing the dental papillae within them, 
and o, the opercula on their borders ; they are 
numbered from 1 to 5 in the order of their first ap- 
pearance ; c, to the inside of each is the lunated 
depression forming the commencement of the germ 
of the corresponding permanent tooth ; a b, line of 
the section shown in fig. 551, 5. 

The sacs and pulps of the ten anterior per- 
manent teeth have their foundations laid 
before birth, behind those of the milk set. 
Recurring to the follicular stage of the tem- 
porary teeth, which is completed about the 

fourteenth week, it will be remembered that behind each milk-follicle there is 
formed a small lunated recess, similar in form to an impression made by the 
nail. As already stated, the mucous membrane lining these recesses escapes 
the general adhesion of the lips and sides of the dental groove, so that when 
the latter closes they are converted into so many cavities, which are called 
by Goodsir, " cavities of reserve." They are ten in number in each jaw, 
and are formed successively from before backwards. They ultimately form 
the sacs for the permanent incisor, canine, and bicuspid teeth. These cavi- 
ties soon elongate and recede into the substance of the gum behind the milk 
follicles, above and behind in the upper jaw, below and behind in the lower. 
In the meantime, a papilla appears in the bottom of each, (that for the 
central incisor appearing first, at about the sixth month,) and one or more 
folds or opercula, as in the case of the temporary teeth, are developed from 
the sides of the cavity, and, by their subsequent union, divide it into two 
portions, the lower portion containing the papilla, and now forming the 
dental sac and pulp of the permanent tooth, and the upper and narrower 
portion being gradually obliterated in the same manner as the primitive 
groove was closed over the milk-sacs. When these changes have taken 
place, the permanent sac adheres to the back of that for the temporary 
tooth. Both of them continue then to grow rapidly, and after a time it is 
found that the bony socket not only forms a cell for the reception of the 
milk-sac, but also a small posterior recess or niche for the permanent sac, 
with which the recess keeps pace in its growth. Confining our description 
now, for convenience, to the lower jaw only, it is found that at length the 
permanent sac so far recedes in the bone as to be lodged in a special osseous 
cavity at some distance below and behind the milk-tooth, the two being com- 
pletely separated from each other by a bony partition. In descending into 

3 u 



802 



THE TEETH. 



the jaw, the permanent sac acquires at first a pear-shap.e, and is then con- 
nected with the gum by a solid membranous pedicle. The recess in the jaw 
has a similar form, drawn out into a long canal for the pedicle, which opens 

Fig. 560. 





II. 



III. 



IV. 



V. 



Fig. 560. SKETCHES SHOWING THE RELATIONS OP THE TEMPORARY AND PERMANENT 
DENTAL SACS AND TEETH (after Blake, with some additions). 

The lower parts of the three first figures, which are somewhat enlarged, represent 
sections of the lower jaw through the alveolus of a temporary incisor tooth : a, indicates 
the sac of the permanent tooth ; c, its pedicle ; 6, the sac of the milk tooth or the milk 
tooth itself ; a', b', indicate the alveolar recesses in which the permanent and temporary 
teeth are lodged, and c, the canal by which that of the former leads to the surface of 
the bone behind the alveolus of the temporary tooth. The fourth and fifth figures, which 
are nearly of the natural size, show the same relations in a more advanced stage, in IV, 
previous to the change of teeth, in V, when the milk-tooth has fallen out and tbe per- 
manent tooth begins to rise in the jaw ; c, the orifice of the bony canal leading to the 
place of the permanent tooth. 

on the edge of the jaw, by an aperture behind the corresponding milk-tooth. 
The permanent tooth is thus separated from the socket of the milk-tooth by 
a bony partition, against which, as well as against the root of the milk-tooth 
just above it, it presses in its rise through the gum, so that these parts are in 
a greater or less extent absorbed. When this has proceeded far enough, the 
milk-tooth becomes loosened, falls out or is removed, and the permanent 
tooth takes its place. The absorption of the dental substance commences 
at or near the ends of the fangs, and proceeds upwards until nothing but 
the crown remains. The cement is first attacked, and then the dentine : 
but the process is similar in the two tissues. The change is not produced 
merely by pressure, but through the agency of a special cellular structure 
developed at the time, and applied to the surface of the tooth. Hollows or 
indentations occur upon the latter, giving it a festooned appearance : and it 
frequently happens that the dental tissues are deposited, absorbed, and 
redeposited alternately in the same tooth (Tomes). The milk-teeth and 
the permanent teeth are said by Serres to be supplied by two different 
arteries, the obliteration of the one belonging to the temporary teeth being 
regarded by him as the cause of their destruction ; but of this there is no 
sufficient proof. 

The six posterior (or " supet added ") permanent teeth, that is, the three 
permanent molars on each side, do not come in the place of other teeth. 
They arise from successive extensions of the dental groove carried backwards 
in the jaw, posterior to the milk-teeth, and named by Goodsir " posterior 
cavities of reserve. " 



DEVELOPMENT OF THE PERMANENT TEETH. 803 

During the general adhesion of the dental groove occurring at the fifteenth 
week, the part posterior to the last temporary molar follicle continues unob- 
literated, and thus forms a cavity of reserve, in the fundus of which a 
papilla ultimately appears, and forms the rudiment of the first permanent 
molar tooth : this takes place very early, viz., at the sixteenth week. The 
deepest part of this cavity is next converted by adhesion into a sac, which 
encloses the papilla, whilst its upper portion elongates backwards so as to 
form another cavity of reserve, in which, at the seventh month after birth, 
the papilla for the second molar tooth appears. After a long interval, during 
which the sac of the first permanent molar and its contained tooth have 
acquired great size, and that of the second molar has also advanced con- 
siderably in development, the same changes once more occur, and give rise to 
the sac and papilla of the wisdom tooth, the rudiments of which are visible 
at the sixth year. The subsequent development of the permanent molar 
teeth takes place from these sacs just like that of the other teeth. 

Calcification begins first in the anterior permanent molar teeth. Its order 
and periods may be thus stated for the upper jaw, the lower being a little 
earlier : First molar, five or six months after birth ; central incisor, a little 
later ; lateral incisor and canine, eight or nine months ; two bicuspids, two 
years or more ; second molar, five or six years ; third molar, or wisdom 
tooth, about twelve years. 



Fig. 561. 




Fig. 561. PART OP THE LOWER JAW OF A CHILD OP THREE OR FOUR YEARS OLD, 

SHOWING THE RELATIONS OP THE TEMPORARY AND PERMANENT TEETH. 

The specimen contains all the milk-teeth of the right side, together with the incisors of 
the left; the inner plate of the jaw has been removed, so as to expose the sacs of all the 
permanent teeth of the right side, except the eighth or wisdom tooth, which is not yet 
formed. The lai'ge sac near the ramus of the jaw is that of the first permanent molar, 
and above and behind it is the commencing rudiment of the second molar. 

Eruption of the permanent teeth. The time at which this occurs in regard 
to each pair of teeth in the lower jaw is exhibited in the subjoined table. 
The corresponding teeth of the upper jaw appear somewhat later. 

Molar, first 6 years. 

Incisors, central . . . . . . . . 7 

lateral ........ 8 

Bicuspids, anterior 9 

,, posterior . , . . . . 10 

Canines 11 to 12 

Molars, second . . . . . . 12 to 13 

third (or wisdom) . . . . 17 to 25 

3 G 2 



804 



THE TEETH. 



It is just before the shedding of the temporary incisors, i. e. , about the 
sixth year, that there is the greatest number of teeth in the jaws. At that 
period there are all the milk-teeth, and all the permanent set except the 
wisdom teeth, making forty-eight. 

Fig. 562. 




Fig. 562. THE TEETH OP A CHILD OP Six YEARS, WITH THE CALCIFIED PARTS OP THE 
PERMANENT TEETH EXPOSED (after Henle aud from nature). 

The whole of the teeth of the right side are shown, together with the three front teeth 
of the left side : in the upper and lower jaws the teeth are indicated as follows, viz. : 
1, milk-teeth i, inner or first incisor ; i', outer or second incisor ; c, canine ; m, first 
molar ; m! second molar. 2, permanent teeth I, inner or first incisor ; 1', outer or 
second incisor; C, canine; B, first bicuspid; B' second bicuspid; M 1 , the first molar, 
which has passed through the gums ; M 2 , the second molar, which has not yet risen above 
the gums : the third molar is not yet formed. 

During the growth of the teeth the jaw increases in depth and length, 
and undergoes changes in form. In the child it is shallow, but it becomes 
much deeper in the adult. In the young subject the alveolar arch describes 
almost the segment of a circle ; but in the adult the curve is semi-elliptical. 
The increase which takes place in the length of the jaw arises from a growth 
behind the position of the milk-teeth, so as to provide room for the three 
additional teeth on each side belonging to the permanent set. At certain 
periods in the growth of the jaws there is not sufficient room in the alveolar 
arch for the growing sacs of the permanent molars ; and hence those parts 
are found at certain stages of their development to be enclosed in the base 
of the coronoid process of the lower jaw, and in the maxillary tuberosity in 
the upper jaw, but they afterwards successively assume their ultimate 
position as the bone increases in length. The space taken up by the ten 



THE TONGUE 805 

anterior permanent teeth very nearly corresponds with that which had been 
occupied by the ten milk-teeth ; the difference in width between the incisors 
of the two sets being compensated for by the smallness of the bicuspids in 
comparison with the milk-molars to which they succeed. Lastly, the angle 
formed by the rarnus and body of the lower jaw differs at different ages ; 
thus it is obtuse in the infant, approaches nearer to a right angle in the 
adult, and again becomes somewhat obtuse in old age. (See p. 52.) 

Relation of the blood-vessels and nerves to the tooth. There is no evidence that the 
blood-vessels send branches into the hard substance. The red stain sometimes 
observed in the teeth, after death by asphyxia, and the red spots occasionally found 
in the dentine, are due to the imbibition of blood effused on the surface of the pulp. 
The dentine formed in young animals fed upon madder is tinged with that colouring 
matter, but this does not appear to take place when the growth of the tooth is com- 
pleted. Nevertheless the tubules of the dentine may serve to convey through its 
substance nutrient fluid poured out by the blood-vessels of the pulp. The teeth are 
sometimes stained yellow in jaundice. 

According to Czermak the primitive nerve-tubules run into the tooth -pulp in 
bundles, which are large towards the centre, and small at the periphery. They lose 
themselves in a plexus at the surface of the pulp. Czermak states that the fibres often 
divide, but that he has not seen loops frequently, and he is doubtful as to the precise 
mode of their termination, 

THE TONGUE. 

The tongue is a muscular organ covered with mucous membrane. By its 
muscular structure it takes part in the processes of mastication and deglu- 
tition, and in the articulation of speech, while its mucous membrane is 
endowed with common sensibility and is the seat of the sense of taste. The 
tongue occupies the concavity of the arch of the lower jaw : posteriorly it is 
connected with the hyoid bone, and the back part of its dorsum forms the 
floor of the arch of the fauces ; inferiorly it receives from base to apex the 
fibres of the genio-glossus muscle, and through the medium of that muscle is 
attached to the lower jaw. 

A. Mucous MEMBRANE. On the under surface of the tongue the mucous 
membrane is smooth and thin. It forms a fold in the middle line, called 
the frcenum lingua, placed in front of the anterior border of the genio-glossi 
muscles. On each side below, as the mucous membrane passes from the 
tongue to the inner surface of the gums, it is reflected over the sublingual 
gland. Not far from the line continued forwards from the frsenum, the 
ranine vein may be distinctly seen through the mucous membrane, and close 
to it lies the ranine artery. Further outwards is an elevated line with a 
fimbriated margin directed outwards, which extends to the tip. The ducts 
of the right and left submaxillary glands end by papillary orifices placed 
close together, one on each side of the freenum ; and further back, in the 
groove between the sides of the tongue and the lower jaw, are found the 
orifices of the several ducts belonging to the sublingual glands. 

The upper surface or dorsum of the tongue is convex in its general out- 
line, and is marked along the middle in its whole length by a slight farrow 
called the raphe, which indicates its bilateral symmetry. About half an 
inch from the base of the tongue, the raphe often terminates in a depres- 
sion, closed at the bottom, which is called the foramen ccecum (Morgagui), 
and in which several mucous glands and follicles open. Three folds, named 
the glosso-epiglottic folds or frseuula, of which the middle one is the largest 
(frsenum epiglottidis), pass backwards from the base of the tongue to the 
epiglottis. The upper surface of the tongue is completely covered with 



806 



THE TONGUE. 



numerous projections or eminences named papillce. They are founl also 
upon the tip and free borders, where, however, they gradually become 
smaller, and disappear towards its under surface. These papillae are dis- 
tinguished into three orders, varying both in size and form. 

Fig. 563. 




Fig. 563. PAPILLAE SURFACE OF THE TONGUE, WITH THE FAUCES AND TONSILS (from 

Sappey). 

1, 2, circumvallate papillae ; in front of 2, the foramen caecum ; 3, fungiform papillae ; 
4, filiform and conical papillae ; 5, transverse and oblique rugae ; 6, mucous glands at 
the base of the tongue and in the fauces ; 7, tonsils ; 8, part of the epiglottis ; 9, median 
glosso-epiglottidean fold or fraenum epiglottidis, 

The large or circumvallate papillae, from seven to twelve in number, are 
found on the back part of the tougue, arranged in two rows, which run 
obliquely backwards and inwards, and meet towards the foramen caecum, like 
the arms of the letter V. They are situated in cup-like cavities or depres- 
sions of the mucous membrane, and have the shape of an inverted cone, of 
which the apex is attached to the bottom of the cavity, and the broad 
flattened base appears on the surface. They are therefore surrounded by a 



PAPILLA OF THE TONGUE. 



807 



circular furrow or trench, around which again is an annular elevation of the 
mucous membrane, covered with the smaller papillae. The exposed surface 
of the papillae vallatse is beset with numerous smaller papillae or filaments ; 



Fig. 564. 



Fig. 564. VERTICAL SECTION 

OF THE ClRCUMVALLATE 

PAPILLAE (from Kolliker). ^ 

A, the papilla ; B, the sur- 
rounding wall; a, the epi- 
thelial covering ; b, the nerves 
of the papilla and wall spread- 
ing towards the surface ; c, 
the secondary papillae. 

and in some of them there 
is found a central depres- 
sion, into which mucous follicles open. 

The middle-sized or fungiform papillse, more numerous than the last, are 
small rounded eminences scattered over the middle and fore part of the 
dorsum of the tongue ; but they are found in great numbers and closer 




Fig. 565. 




Fig. 565. SURFACE AND SECTION OF THE FUNGI- 
FORM PAPILLA (from Kolliker after Todd and 
Bowman). 

A, the surface of a fungiform papilla partially 
denuded of its epithelium, ^ ; p, secondary 
papillse ; e, epithelium. 

B, section of a fungiform papilla with the 
blood-vessels injected, a, artery ; v, vein ; c, 
capillary loops of simple papillaa in the neigh- 
bouring structure of the tongue ; d, capillary 
loops of the secondary papilla? ; e, epithelium., 



together at the apex and upon the bor- 
ders. They are easily distinguished in 
the living tongue by their deeper red 
colour. They are narrow at their point 
of attachment, but are gradually enlarged 
towards their free extremities, which are 
blunt and rounded, and are covered with 
smaller filamentous appendages or papillae. 
The smallest papilhe, conical and fili- 
form, are the most numerous of all. They 
are minute, conical, tapering, or cylin- 
drical processes, which are densely packed 
over the greater part of the dorsum of the 
tongue, but towards the base gradually 

disappear. They are arranged in lines, which correspond at first with the 
oblique direction of the two ridges of the papillae vallatae, frit gradually be- 
come transverse towards the tip of the tongue. At the sides they are longer 
and more filiform, and arranged in parallel rows, perpendicular to the border 
of the tongue. 

Considerable variety occurs in the appearance of the papillze on the tongues ot 
different persons. Thus occasionally instances occur in which the tongue has a 
quite smooth appearance, and others are seen in which numbers of the filiform papillae 
are elongated into the appearance of short brown hairs, as shown in Fig. 566. 




808 



THE TONGUE, 



When examined microscopically in sections, all the kinds of papillee now 
described are observed to be bearers of closely set secondary papillae. The 
secondary papillae are the structures which correspond with the papillae of 
the general integument, and are occupied each by a long loop of capillary 
blood-vessel. Simple papillae of the same description are likewise inter- 
spersed between the three large kinds, and are found on the back part of 

Fig. 566. Two FILIFORM PAPILLAE, 
ONE WITH EPITHELIUM, THE OTHER 
WITHOUT (from Kolliker, after 
Todd and Bowman). ^ 

p, the substance of the papillae di- 
viding at their upper extremities into 
secondary papillae ; a, artery, and v, 
vein, dividing into capillary loops ; 
e, epithelial covering, laminated be- 
tween the papillae, but extended into 
hair-like processes /, from the ex- 
tremities of the secondary papillae. 

the tongue, behind the circum- 
vallate range, as well as covering 
the under surface of the tongue 
and the rest of the mucous mem- 
brane of the mouth. The epi- 
thelium covering the tongue, 
like that of the mouth generally, 
is of the squamous kind. It is 
of considerable thickness, and 
the simple papillae, together with 
the secondary papillae surmount- 
ing those of the circumvallate 
and fungiform kinds, are con- 
cealed beneath it, or nearly so. 
But the secondary papillae, borne 
by those of the filiform kind, 
are peculiar both in contain- 
ing a number of elastic fibres, 

which give them greater firmness, and in the character of their epithelial 
covering, which is dense and imbricated, and which forms a separate process 
over each, greater in length than the papilla which it covers. Over some 
of the filiform papilla these processes form a pencil of fine fibres ; and on 
others they approach closely in character and structure to hairs. The papillae 
are undoubtedly the parts chiefly concerned in the special sense of taste ; 
but they also possess, in a very acute degree, common tactile sensibility ; 
and the filiform papillae, armed with their denser epithelial covering, serve 
a mechanical use, in the action of the tongue upon the food, as is well 
illustrated by the more developed form which these papillae attain in many 
carnivorous animals. The papillary surface of the tongue is supplied abun- 
dantly with nerves. It is difficult to trace the nerve- fibres in the papillae 
filiformes, owing to the presence of elastic filaments. In the papi